Revista Mexicana de Ciencias Geológicas ISSN: 1026-8774 [email protected] Universidad Nacional Autónoma de México México

Ferrusquía-Villafranca, Ismael; Ruiz-González, José E. Isotope geochronology and vertebrate paleontology in Mexico: Panorama and critical appraisal Revista Mexicana de Ciencias Geológicas, vol. 32, núm. 2, 2015, pp. 323-342 Universidad Nacional Autónoma de México Querétaro, México

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How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative REVISTA MEXICANA DE CIENCIAS GEOLÓGICAS Isotope geochronology and vertebratev. paleontology32, núm. 2, 2015, in p. México 323-342

Isotope geochronology and vertebrate paleontology in Mexico: Panorama and critical appraisal

Ismael Ferrusquía-Villafranca* and José E. Ruiz-González

Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Del. Coyoacán, C.P. 45100, México, D.F., Mexico. * [email protected]

ABSTRACT The pliocene GTO 43, Rancho El Ocote, GTO 2D, Garbani, GTO 11, Pantera, GTO 12B, Estancia, GTO 5A, Rancho El Ocote, The combined isotopic/paleontologic approach drove a qualitative GTO 55 sites (CeP), Santa María Amajac, Charo and Buenaventura sites leap in understanding Earth’s geologic history/evolution, yet, in spite (TMVB) record a 4.5–3.5 Ma tectonic/volcanic activity; their Blancan of its early start, it is still not widely used in México. Here we report 28 chronofauna includes numerous South American taxa, disclosing that sites where such an approach was applied; their space/time distribution the Great American Biotic Interchange reached its peak. These sites/ is uneven, leaving morphotectonic provinces and/or geochronologic sequences also carry Late Hemphillian taxa, thus allowing studying intervals little or not studied at all. The sites are located in eight mammalian succession and turnover in central Mexico. morphotectonic provinces, their age spans the Jurassic-Pliocene as Finally, in the 27 reported sites with isotopic ages and studied follows: Baja California Península (BCP), one Cretaceous and one Cretaceous-Tertiary vertebrates, the North American Land Mammal Miocene site. Northwestern Ranges, Basins and Plains (NW), one Age System is proven supporting the uncritical belief that it is appro- Miocene site. Sierra Madre Occidental (SMOc), four Miocene sites. priate to date faunas from Mexico, in spite that this system is based on Central Plateau (CeP), one Late Eocene and eight Miocene/Pliocene mammal faunas from temperate/cold North America. sites. Sierra Madre Oriental (SMOr), one Jurassic and one Miocene sites. Trans-Mexican Volcanic Belt (TMVB), two Miocene and three Key words: Mexico; geochronology; vertebrate paleontology; Cenozoic; Pliocene sites. Sierra Madre del Sur (SMS), one Eocene and three Cretaceous; Jurassic. Miocene sites. Sierra Madre de Chiapas (SMCh), one Miocene site. The Chihuahua-Coahuila sierras, basins and plateaus, Gulf Coastal Plain and Yucatan Platform lack such sites. RESUMEN The Pliensbachian Huizachal site (SMOr) lies in the rift system that split central-eastern Pangea and contains Mexico’s oldest vertebrate El enfoque isotópico/paleontológico combinado impulsó un salto fauna. The Late Campanian El Rosario site (BCP) is located in the cualitativo en el entendimiento de la historia/evolución de la Tierra, namesake Forearc Basin, its fauna shows moderate endemism. The empero, no se utiliza ampliamente en México a pesar de su temprano Cenozoic sites lie in graben structures and record episodes of tectonic inicio. Reportamos aquí 28 sitios donde se empleó este enfoque; su and magmatic activity. The Eocene Marfil (CeP) and Yolomécatl (SMS) distribución espacio/temporal es irregular, quedando provincias mor- sites occur in post-Laramide basins, their Bridgerian and Duchesnian/ fotectónicas y/o intervalos geocronológicos poco o nada estudiados. Chadronian faunas show boreal affinities and strong endemism. The Los sitios yacen en ocho provincias morfotectónicas y abarcan del Early Miocene Tubutama (NW) and Suchilquitongo (SMS) sites record Jurásico al Plioceno: Península de Baja California (BCP), un sitio del tectonic/magmatic activity around 20 Ma, and their faunas display Cretácico y uno del Mioceno. Sierras, cuencas y planicies del Noroeste North American affinities and moderate endemism. (NW), uno del Mioceno. Sierra Madre Occidental (SMOc), cuatro del The Middle Miocene La Purísima (BCP), Matatlán (SMS), El Mioceno. Altiplanicie Central (CeP), uno del Eoceno Tardío y ocho del Camarón (SMS) and Ixtapa (SMCh) sites record tectonic and magmatic Mioceno/Plioceno. Sierra Madre Oriental (SMOr), uno Jurásico y uno activity circa 15 Ma; the three latter ones disclose a volcanic belt del Mioceno. Faja Volcánica Trans-Mexicana (TMVB), dos del Mioceno extending from central Oaxaca to northern Chiapas; their faunas y tres del Plioceno. Sierra Madre del Sur (SMS), uno del Eoceno y tres show North American affinities and evidence local cladogenesis. del Mioceno. Sierra Madre de Chiapas (SMCh), uno del Mioceno. Las The Late Miocene Paso del Águila (SMOr), El Resbalón, Cofradía, cuencas, sierras y mesetas de Chihuahua-Coahuila, Planicie Costera del Tepezalá, El Trapiche (SMOc), Rancho El Ocote (CeP) and Tecolotlán Golfo, y Plataforma de Yucatán carecen de tales sitios. (TMVB) sites record tectonic/magmatic activity between 9.5 and 5.0 El sitio Pliensbachiano Huizachal (SMOr) yace en el rift que di- Ma; their mammals involve Late Clarendonian-Early Hemphillian vidió Pangea centro-oriental y porta la vertebradofauna más antigua and Hemphillian chronofaunas. The younger fauna reveals an early de México. El sitio Campaniano Tardío El Rosario está en la Cuenca appearance of South American taxa in North America. The important de Antearco homónima, su fauna muestra endemismo moderado. Los Chapala site (TMVB) still lacks isotopic ages associated to Late Tertiary sitios cenozoicos se encuentran en fosas tectónicas y registran episodios vertebrates. de actividad tectónica/magmática. Los sitios Marfil (CeP) y Yolomécatl

Ferrusquía-Villafranca, I., Ruiz-González, J.E., 2015, Isotope geochronology and vertebrate paleontology in Mexico: Panorama and critical appraisal: Revista Mexicana de Ciencias Geológicas, v. 32, núm. 2, p. 323-342.

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(SMS) están en cuencas postlaramídicas, sus faunas Bridgeriana y in the northern part and ~15 Ma in the southeastern part), Oaxacan Duchesniano/Chadronianas muestran afinidad boreal y endemismo. Subisthmian region (~15 Ma), Oaxacan Isthmian region (~15 Ma), and Los sitios temprano-micénicos Tubutama (NW) y Suchilquitongo (SMS) northwestern Chiapas (~15 Ma). Such data allowed to calibrate three registran actividad tectónica/magmática alrededor de 20 Ma, sus faunas local faunas from Oaxaca (Suchilquitongo, 20 Ma; Matatlán, ~15 Ma) tienen afinidad boreal y endemismo moderado. and one from Chiapas (Ixtapa, 15 ~Ma). The geologic and paleobio- Los sitios mesomiocénicos La Purísima (BCP), Matatlán, El Camarón logical significance of such discoveries will be discussed elsewhere. (SMS) e Ixtapa (SMCh) registran actividad tectónica/magmática cercana In the last decades, similar efforts to date other vertebrate-bearing a 15 Ma; los tres últimos evidencian una faja volcánica extendida desde sequences have been carried out yielding important results, such as Oaxaca central a Chiapas septentrional; sus faunas tienen afinidad boreal an Early Jurassic sequence in Tamaulipas, Sierra Madre Oriental MP y cladogénesis local. Los sitios tardimiocénicos Paso del Águila (SMOr), (Fastovsky et al., 1998, 2005), a Late Cretaceous sequence in Baja El Resbalón, Cofradía, Tepezalá, El Trapiche (SMOc), Rancho El Ocote California, Península de Baja California MP (Renne et al., 1991), an (CeP) y Tecolotlán (TMVB), registran actividad tectónica/magmática Early Paleogene sequence and fauna in Guanajuato, Central Plateau de hace unos 9.5–5.0 Ma; sus mamíferos involucran las cronofaunas MP (Aranda-Gómez and McDowell, 1998), Late Neogene sequences Clarendoniano-Hemphilliana y Hemphilliana, esta última revela la from selected areas of the Trans-Mexican Volcanic Belt MP and neigh- aparición temprana de taxa sudamericanos en Norteamérica. El im- boring regions of the Central Plateau MP (Carranza-Castañeda, 2006 portante sitio Chapala aún carece de fechamientos isotópicos asociados and references therein) and lately in the Sierra Madre Oriental MP. a vertebrados tarditerciarios. The geologic and paleobiologic significance will be discussed in the Los sitios pliocénicos GTO 43, Rancho El Ocote, GTO 2D, Garbani, section dealing with each fauna. GTO 11, Pantera, GTO 12B, Estancia, GTO 5A, Rancho El Ocote, It should be noted that the geologic part of all these results varies GTO 55 (CeP), Santa María Amajac, Charo y Buenaventura (TMVB) enormously due to: (1) differences in the formality/depth given to the registran actividad tectónica/volcánica próxima a 4.5–3.5 Ma; su cro- treatment of each sequence. (2) Intrinsic differences of each sequence, nofauna Blancana incluye numerosos taxa sudamericanos, indicando so that some bear vertebrates or dated rock material at more than one así el apogeo del Gran Intercambio Biótico Americano. Estos(as) sitios/ stratigraphic level. (3) More than one research team may have studied sequencias portan también taxa hemphillianos, permitiendo entonces a given sequence. These facts may lead to confusion or ambiguity. To estudiar la sucesión y el reemplazamiento faunístico en México central. avoid these discrepancies, we deem it appropriate to describe each Finalmente, en los 27 sitios reportados con fechas isotópicas y en sequence in an uniform way and to evaluate the nomenclatorial status los vertebrados tardicretácico-terciarios estudiados, el Sistema North of the units with vertebrates and/or dated rock material. Both items American Land Mammal Ages se corroboró, apoyando así la suposición influence the dependability of analyzed results. de su idoneidad para fechar mastofaunas de México, a pesar de estar The possibility to test the North American Land Mammal Age basado en faunas de Norteamérica templada/fría. (NALMA) System’s aptness to date faunas from 28 sites scattered throughout Mexico, is an added bonus. Such possibility is at present Palabras clave: México; geocronología; paleontología de vertebrados; taken for granted, notwithstanding these facts: (1) it is based on Cenozoico; Cretácico; Jurásico. the occurrence of bioevents (certain mammal taxa) in temperate (30°–50°N Latitud) North America (i.e., the contiguous United States; cf. Woodburne, 2004). (2) The occurrence of some taxa in Central INTRODUCTION Mexico and Alaska that does not conform to it (cf. Bell et al., 2004). Given the above, we aim at fulfilling the following objectives: Paleontology (particularly vertebrate paleontology) benefitted im- 1. To critically present and review the geologic and vertebrate mensely from the advent of isotopic dating at accessible price that oc- paleontologic information on the sites where this dual isotopic/ curred in the early sixties. It allowed calibration of the Geochronologic paleontologic approach has been applied during the last fifty years Time-table (Time-scale), which up to then was based on bioevents, such in this country. as the first/last occurrences of significant selected taxa (e.g. fusulinids, 2. To test by this review if the North American Land Mammal Age ammonites, planctonic foraminifers and terrestrial tetrapods, largely System is suitable to date vertebrate faunas in Mexico. mammals). This, in turn, made possible a more precise long range cor- 3. To contribute to a better understanding of this country’s verte- relation of geologic events s.l. across distant regions/continents, thus brate faunistic evolution, and to a lesser extent, its geologic evolution producing a qualitative leap in the understanding of the history and as well. evolution of the Earth System, and of the living beings that populate it. The application of isotopic dating techniques started early in México, with the foundation in 1962 of the Laboratorio de Geocronometría, METHODOLOGY Instituto de Geología, Universidad Nacional Autónoma de México, which mainly focused on dating Precambrian, Paleozoic and Mesozoic In Figure 1 and Table 1 we present the results of an exhaustive events. The Mixteca region, northwestern Oaxaca state in the Sierra bibliographic search for isotopically dated lithostratigraphic units that Madre del Sur Morphotectonic Province (MP hereafter) was one of the bear studied vertebrate fossil assemblages, or that are stratigraphically first, where isotopic dating of Cenozoic events was attempted during related to such units, thus furnishing their minimal/maximal ages. the development of the senior author’s doctoral dissertation in the Across the country, we detected 28 pre-Pleistocene sites that fulfill this University of Texas at Austin (Ferrusquía-Villafranca, 1971), through dual criterion, from which reliable analyses can be made. the cooperation of Professors Leon Long and Fred McDowell. The sites are plotted on a morphotectonic provinces (MP) map of The systematic effort to isotopically date actually or potentially México (cf. Ferrusquía-Villafranca et al., 2010), because the geological vertebrate-bearing Cenozoic continental sequences was carried out significance of the sites-information could be perceived better there, by means of a far-reaching multidisciplinary and multi-institutional than in a political division-state map. The sites are listed in Table 1, research project. This study produced K-Ar ages in selected areas which includes eight information items (columns); they are explained from the Mixteca region, Oaxaca (~30 Ma), Valle de Oaxaca (~20 Ma as follows:

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o o o o o o o 114 108 102 96 90 32 32

L E G E N D 5 TERTIARY 2 CRETACEOUS JURASSIC

1. CAÑÓN DE HUIZACHAL, TAMPS. 2. EL ROSA- o 28o RIO, B.C. 3. MARFÍL, GTO. 4. YOLOMÉCATL, OAX. 28 5. TUBUTAMA, SON. 6. SUCHILQUITONGO, OAX. 7. MATATLÁN, OAX. 8. IXTAPA, CHIS. 9. NEJAPA, OAX. 10. LA PURÍSIMA, B.C.S. 11. PASO DEL ÁGUI- 10 LA, SLP. 12. CHAPALA, JAL. 13. TEPEZALÁ AREA, ZAC. 14. COFRADÍA AREA, ZAC. 15. EL RESBALÓN AREA, ZAC. 16. EL TRAPICHE, NAY. 17. RANCHO EL OCOTE, GTO. 18. TECOLOTLÁN, JAL. 19. GTO 43, GTO. 20. GARBANI, GTO. 21. LA PANTERA, o o 24 GTO. 22. ESTANCIA, GTO. 23. SANTA MARÍA AMA- 24 JAC, HGO. 24. CHARO, MICH. 25. BUENAVENTURA, N 1 JAL. 11 1314 16 19-22 15 NW 0 Km 500 o o 3 17 20 3 20 BCP CH-CO 25 SMOc 18 12 24 23 GCP SMOr CeP 4 YPL 6 TMVB o o 7 8 16 9 16 GCP SMS SMCh

114o 108o 102o 96o 90o

Figure1. Morphotectonic Provinces Map of Mexico showing the location of sites with isotopically dated lithostratigraphic units that bear vertebrates, plotted on a satellite image. [Source of image: CONABIO (2003)].

(a) Geographic-Geologic: The first column indicates the morpho- (2004), the standard reference for mammalian biochronology. The tectonic province and the state to which the site belongs, each received eighth column carries the geochronologic information expressed in a consecutive number; a site may include a single locality or a cluster of epochs and periods sensu Gradstein et al. (2004). spatially close localities, which are designated area sites. The chief ref- (d) Footnotes at the end of Table 1: they explain symbols and erences (both isotopical and paleontological) are given too (bracketed provide bibliographic references to the isotope geochronology data number after the site-name) and spelled out as foot notes. The second (RCH), and the biochronological (BCH) data; both are keyed to the column shows the fossil-bearing unit name from which isotopic ages bracketed number on the right of the first column. Notice that in were obtained; the unit’s condition (named or unnamed) is stated; the some instances, two or more sites may carry the same bibliographic named units are classified as formal or informal, depending on whether reference number; this indicates that in the corresponding paper, more or not their proposal fulfills the requirements of the North American than one site was studied. On the other hand, the same site could have Stratigraphic Code (NACSN, 2005) or of the pertinent code at the been independently studied by two or more different research teams, time of their proposal. The third column gives the site coordinates accordingly we have cited all papers involved, giving them independent as stated in the corresponding paper or as inferred from information bibliographic reference numbers; in the text we discuss and parsimoni- given there; this last mode is expressed by the sign & as an exponent. ously assess them. (b) Isotopic Geochronologic: The fourth column bears the nu- merical ages. The fifth column states the dating method (K-Ar e.g. Terms, abbreviations and considerations Bonhomme et al., 1975; 40Ar-39Ar, e.g. van der Pluijm et al., 2006; U-Pb, The boundaries of epochs/stages are taken from Gradstein et al. e.g. Gehrels et al., 2008; fission track, e.g. Wagner and Van den Haute, (2004). The sedimentary petrographic nomenclature follows Folk 1992) and the mineral used; in some instances, the latter was not stated (1974) and Boggs (1995), the pyroclastic terminology used is from in the corresponding paper. Fisher and Schmincke (1984), the sedimentary facies nomenclature (c) Paleontologic-Geochronologic: The sixth column lists the follows Miall (2006, 2010) for the fluvial facies and Collinson (1996) names of the fossil assemblages studied, they may be a fauna (f., an for the lacustrine facies. In some instances, old descriptions were assemblage collected from several spatially close localities that lie in a rediscribed/interpreted in current terminology and/or conceptions. given area or region), local fauna (l.f., an assemblage collected from a The Morphotectonic Province boundaries were taken from Ferrusquía- single locality, or spatially very close localities) and single occurrence Villafranca et al. (2010). [s.o., vertebrate remain(s) that belong to a single individual/taxon]. Such assemblages are usually named after a geographic s.l. feature. The Morphotectonic province abbreviations seventh column shows the biochronological age of each assemblage, BCP, Baja California Peninsula; NW, Northwestern plains and which apart from the Jurassic, is stated in terms of the North American sierras; SMOc, Sierra Madre Occidental; CH-CO, Chihuahua-Coahuila Land Mammal Ages (acronymed NALMA) as presented in Woodburne plateaus and ranges; SMOr, Sierra Madre Oriental; GCP, Gulf Coastal

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Table 1. Isotopically dated Jurassic, Cretaceous and Tertiary lithostratigraphic units from Mexico that bear studied vertebrates.

Site (Ref.) Formation &Site Radio-isotopic Method #Fauna (f) or NALMA* Epoch** Morphotectonic Province Coordinates age (in Ma) Local Fauna or Stage/Age** or Period** State (l.f.)

1. Cañón de Huizachal (1a) La Boca 23°35’N–99°14’W& 186±2 U-Pb (Zircon) La Boca l.f. Middle Pliensbachian Early Sierra Madre Oriental M.P Jurassic Tamaulipas State (1b) 23°35’N–99°14’W& 189.0±0.2 206Pb/238U vs. earliest Pliensbachian 207Pb/235U concor- dia plot (Zircon) (1c) 23°35’N–99°14’W& 183.4±0.9 U-Pb (Zircon) Late Pliensbachian WMA (1c) 23°35’N–99°14’W& 184.2±1.2 U-Pb (Zircón) Late Pliensbachian WMA 2. El Rosario (2) El Gallo 30°03’N–115°44’W 73.59±0.09 40Ar-39Ar El Rosario l.f. Late Judithian Late Baja California Peninsula (Sanidine) (Late Campanian) Cretaceous M.P. 30°02’N–115°45’W 74.21±0.15 40Ar-39Ar Baja California State (Sanidine) 30°02’N–115°43’W 74.25±0.07 40Ar-39Ar (Sanidine) 30°02’N–115°46’W 74.46±0.08 40Ar-39Ar (Sanidine) 29°58’N–115°43’W 74.87±=.05 40Ar-39Ar (Sanidine) 3. Marfil (3) Guanajuato 20°59’N–101°17’W 49.3±1.0 40K-40Ar Marfil l.f. Early-Middle Early Central Plateau M.P. Conglomerate (Whole rock) Bridgerian Eocene Guanajuato State (interbedded lava flow) 4. Yolomécatl (4a) Yanhuitlán 17°30’N–97°20’W 49.0±8.0 Pb α Yanhuitlán Late Tiffanian- Late Sierra Madre del Sur M.P. (Zircon) Early Uintan Paleocene- Oaxaca State Middle Eocene (4b) An unnamed 17°34’05”–97°23’36” 40.5±1.7 40K-40Ar Late Laccolith (Hornblende) Eocene (4C) Same unnamed 17°34.05’– 43.0±1.2 40K-40Ar late Laccolith 97°23.6167’ (Best estímate) (Plagioclase) Middle Eocene (4d) Cañada María 17°41’–97°16’ 35.7±1.0 40K-40Ar Andesite (Informal) (whole rock) latest Eocene 5. Tubutama (5) Unnamed 31°00’–111°30’ 22.3±0.08 40K-40Ar Tubutama s.o. Early Hemingfordian Earliest Northwestern Plains and (it might be Miocene Sierras M.P. an age open to Sonora State question) 6. Suchilquitongo (6) Suchilquitongo, Etla 17°12’N–96°47’W 19.2±0.5 40K-40Ar Suchilquitongo latestest Arikareean Early Sierra Madre del Sur M.P. Ignimbrite Member (Plagioclase) (Ar4) Miocene Oaxaca State 17°47’N–96°47’W 20.3±0.4 Late Arikareean (Ar3) 40K-40Ar (Biotite) 7. Matatlán (7) Mitla Tuff 16°58’N–96°18’W 15.3±0.8 40K-40Ar Matatlán Early Barstovian (Ba1) early Sierra Madre del Sur M.P. (Plagioclase) Middle Oaxaca State 16°58’N–96°18’W 16.0±0.8 40K-40Ar earliest Barstovian- Miocene (Biotite) latest Arikareean 8. Ixtapa (8) Ixtapa 16°50’N–92°54’W 15.02±0.35 40K-40Ar (Biotite) Ixtapa l.f. Early Barstovian (Ba1) early Sierra Madre de Chiapas est Barstoian-lst Arik- Middle M.P. 16°50’N–92°54’W 16.02±0.53 40K-40Ar areean Miocene Chiapas State (Plagioclase) 9. Nejapa (9) Yautepec 16°38’N–96°02’W 14.96±0.85 40K-40Ar Nejapa Early Barstovian (Ba1) early Sierra Madre del Sur M.P. Tuff (Plagioclase) Middle Oaxaca State 16°38’N–96°02’W 15.78±0.37 40K-40Ar earliest Barstovian (Ba1) Miocene (Plagioclase) 16°38’N–96°02’W 15.82±0.37 40K-40Ar earliest Barstovian (Ba1) (Plagioclase) continues

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Table 1 (cont.). Isotopically dated Jurassic, Cretaceous and Tertiary lithostratigraphic units from Mexico that bear studied vertebrates.

Site (Ref.) Formation &Site Radio-isotopic Method #Fauna (f) or NALMA* Epoch** Morphotectonic Province Coordinates age (in Ma) Local Fauna or Stage/Age** or Period** State (l.f.)

10. La Purísima (10a) Comundú 26°09’N–112°07’W 14.5±0.9 40K-40Ar La Purísima l.f. Barstovian Late Baja California Peninsula Miocene M.P. 13.0±0.25 Baja California (10 b) Comondú “Group” Not Given 12.36±016 40Ar-39Ar Early Late Sur State (Alf) (Plagioclase) Clarendonian Miocene Not Given 13.77±0.10 40Ar-39Ar Barstovian Middle (Alf) (Hornblende) Miocene Not Given 14.08±0.20 40Ar-39Ar Barstovian Middle (Alf) (Plagioclase) Miocene Not Given 14.67±0.09 40Ar-39Ar Barstovian Middle (Adi) (Hornblende) Miocene Not Given 20.27±0.08 40Ar-39Ar Late Arikareean Early (Biotite) Miocene (10c) Comondú 24°03’N–110°34’W 9.0 U-Pb Clarendonian Late “Group” (tuff) (Zircon) Miocene Comondú Cummulative “Group” probability plot 11. Paso del Águila (11) San Nicolás 22°17’N–100°36’W 10.99±0.22 40Ar-39Ar (Glass) Paso del Águila Middle Clarendonian Late Sierra Madre Oriental M.P. l.f. (Cl2) Miocene San Luis Potosí State 22°17’N–100°34’W 7.41±0.31 40Ar-39Ar (Glass) Early Hemphillian (Hh1) 12. Chapala (12a) Unnamed 20°18’N–103°12’W& 7.0±0.3 40Ar-39Ar No fauna Late Trans-Mexican Volcanic (Laccolith) (Minimal age) associated Miocene Belt M.P. (12a) Unnamed (tuff 5.2±0.3 40Ar-39Ar No fauna earliest Jalisco State sheet within the associated Pliocene sedimentary #(Chapala f.) sequence)) (12b) Chapala Group 6.2±0.2 40K-40Ar No fauna Late (Informal, it is a (Minimal age) associated Miocene rhyolithic flow #(Chapala f.) succession) (12b) Chapala 3.4±0.2 40K-40Ar No fauna Middle (Informal; basal (Maximal age) associated Pliocene lava flow) #(Chapala f.) 13. Tepezalá Area (13) 21°38’N–103°01’W& 6.95±0.27 U-Pb (Zircon) Tepezalá l.f. Late Hemphillian Late Sierra Madre Occidental WMA (Hh2) Miocene M.P. Zacatecas State 14. Cofradía Area (13) 21°33’N–103°02’W& 6.53±0.11 U-Pb (Zircon) Cofradía l.f. Late Hemphillian Late Sierra Madre Occidental WMA (Hh3) Miocene M.P. Zacatecas State Juchipila Juchipila f. 15. El Resbalón Area (13) Juchipila 21°22’N–103°07’W& 5.59±0.11 U (Zircon) El Resbalón l.f. latest Hemphillian latest Sierra Madre Occidental (Informal) WMA (Hh4) Miocene M.P. Zacatecas State 16. El Trapiche (13) Unnamed 21°26’N–104°12’W& 5.50±0.05 205Pb/238U (Zircon) Trapiche l.f. latest Hemphillian latest Sierra Madre Occidental WMA (Hh4) Miocene M.P. 21°17’N–104°12’W& 5.12±0.26 206Pb/238U El Trapiche l.f. Late Hemphillian (Hh4) Nayarit State (Zircon) WMA San Miguel de Allende 17. Rancho El Ocote Unnamed 21°05’N–100°41’W& 5.7±0.4 Fission Track Rancho El Late Hemphillian latest (=REO), GTO 2A (14a) (Zircon) Ocote l.f. (Hh4) Miocene REO, GTO 2C (14a) 21°05’N–100°41’W& 4.8±0.2 Fission Track earliest Blancan Early (Zircon) Blancan I Pliocene REO, GTO 2D (14b) 21°05’N–100°41’W& 4.7±0.07 40Ar-39Ar earliest Blancan Early (Sanidine) (Blancan I) Pliocene REO, GTO 2D (14b) 21°05’N–100°41’W& 4.747±0.032 40Ar-39Ar Early Blancan Early Central Plateau M.P. (Sanidine) (Blancan I) Pliocene Guanajuato State continues

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Table 1 (cont.). Isotopically dated Jurassic, Cretaceous and Tertiary lithostratigraphic units from Mexico that bear studied vertebrates.

Site (Ref.) Formation &Site Radio-isotopic Method #Fauna (f) or NALMA* Epoch** Morphotectonic Province Coordinates age (in Ma) Local Fauna or Stage/Age** or Period** State (l.f.)

18. Tecolotlán (14b) Unnamed 20°12’N–104°01’W& 4.89±0.16 40Ar-39Ar Tecolotlán l.f. latest Hemphillian Early Trans-Mexican Volcanic Belt Pliocene M.P. (14b) 20°13’N–104°01’W& 4.938±0.16 40Ar-39Ar latest Hemphillian Early Jalisco State Pliocene 19. GTO 43 (14a) 21°03’N–100°47’W& 4.4 ±0.3 Fission Track Rinconada l.f. Early Blancan Early (Zircon) (Blancan II) Pliocene REO, GTO 2D (14a) 21°05’N–100°41’W& 4.6±0.3 Fission Track Rancho El Early Blancan Early Central Plateau M.P. (Zircón) Ocote (Blancan II) Pliocene Guanajuato State 20. Garbani, GTO 11 (14a) 21°01’’N–100°46’W 4.1±0.5 Fission Track Garbani l.f. Early Blancan Early Central Plateau M.P. (Zircon) (Blancan III) Pliocene Guanajuato State 21. La Pantera, GTO 12B 21°03’N–100°46’W& 3.9±0.3 Fission Track La Pantera l.f. Early Blancan Early Central Plateau M.P. (14a) (Zircón) (Blancan III) Pliocene Guanajuato State 22. Estancia, GTO 5A (14b) 21°03’N–100°45’W& 3.32±0.02 40Ar-39Ar Estancia l.f. Middle Blancan Middle Central Plateau M.P. (Sanidine) (Blancan III) Pliocene Guanajuato State 17. REO, GTO 55 (14b) 21°05’N–100°41’W& 3.08±0.5 Fission Track Rancho El Middle Blancan Middle Central Plateau M.P. (Zircon) Ocote (Blancan III) Pliocene Guanajuato State 23. Santa María Amajac “Atotonilco El 20°36’N–98°42’W& 4.2±0.3 Fission Track Amajac l.f. Middle Blancan Early Trans-Mexican (14a) Grande Formation” (Zircon) (Blancan II) Pliocene Volcanic Belt M.P. (Informal) Hidalgo State (14b) 20°36’N–98°42’W& 4.57±0.02 40Ar-39Ar Early Blancan Early (Sanidine) (Blancan II) Pliocene

(14b) 20°36’N–98°42’W& 4.591±0.007 40Ar-39Ar Early Blancan Early (Sanidine) (Blancan II) Pliocene 24. Charo (14-15) Unamed 19°44’N–101°03’W& 3.6±0.3 Fission Track La Goleta l.f. Middle Blancan Middle Trans-Mexican Volcanic Belt (Blancan III) Pliocene M.P. (14c) 19°45’N–101°03’W& 3.6 40K-39Ar Middle Blancan Middle Michoacán State (Blancan III) Pliocene 25. Buenaventura (13) Unnamed 20°09’N–104°05’W& 2.6±0.2 Fission Track Buenaventura Late Blancan Late Trans-Mexican Volcanic (Zircon) l.f. (Blancan IV) Pliocene Belt M.P. Jalisco State

ABBREVIATIONS: Alf: Andesitic lava flow. Adi: andesitic dike. BCH: biochronologic reference [indicated by number in brackets beside the site name]. RCH, radio-isotopic reference [indicated by number in brackets beside the locality name]. NALMA: North American Land Mammal Age. WMA: weighted mean age.

SYMBOLS: *Geochronometric NALMA boundaries after Woodburne (2004), particularly Cifelli et al. (2004, Judithian, Late Cretaceous), Robinson et al. (2004, Wasatchian-Duchesnian, Eocene), Tedford et al. (2004, Arikareean-Clarendonian, Early-Middle Miocene), Bell et al. (2004, Blancan-Rancholabrean, Late Pliocene- Pleistocene). **Geochronometric Period, Stage/Age, and Epoch boundaries after Gradstein et al. (2004). & Latitude-Longitud of RCH sampling site not stated by author; coordinates inferred from information presented in the corresponding article. #Attributed fauna, i.e., a fauna or faunal assemblage known to occur in the area/locality, but not present in the dated/sampled section .

REFERENCES: [RCH1]: 1a, Fastovsky et al. (1998); 1b, Fastovsky et al. (2005); 1c, Rubio-Cisneros et al. (2011). [BCH1]: Clark and Hopson (1985), Clark et al. (1994), Fastovsky et al. 1995). [RCH2]: Renne et al. (1991); [BCH2]: Molnar (1974), Morris (1972, 1973a-b, 1981); Lillegraben (1972, 1976). [RCH3]: Aranda-Gómez and McDowell (1998). [BCH3]: Fries et al. (1955), Ferrusquía-Villafranca (1989, 2004, 2005). [RCH4]: 4a. Ferrusquía-Villafranca (1976). 4b. Martiny et al. (2000). 4c. Cerca et al. (2007). 4d. Santamaría-Díaz et al. (2008). [BCH4]: Jiménez-Hidalgo et al. (2011). [RCH5]: Arriaga-Meléndez et al. (1986). [BCH5]: Ferrusquía- Villafranca (1990a). [RCH6]: Ferrusquía-Villafranca and McDowell (1991). [BCH6]: Ferrusquía-Villafranca (1990a, 2003). [RCH7]: Ferrusquía-Villafranca and McDowell (1991), [BCH7]: Ferrusquía-Villafranca (1990a, 2003). [RCH8]: Ferrusquía-Villafranca (1996). [BCH8]: Ferrusquía-Villafranca (1990b, 2003). [RCH9]: Ferrusquía-Villafranca (2001). [BCH9]: Ferrusquía-Villafranca (1990b, 2003). [RCH10]: 10a. Mc Lean et al. (1987). 10b. Umhoefer et al. (2001). 10c. Fletcher et al. (2007). [BCH10]: Ferrusquía-Villafranca (1990a). [RCH11]: Ferrusquía-Villafranca et al. (2015). [BCH11]: Ferrusquía-Villafranca et al. (2014). [RCH12a]: Israde-Alcántara et al. (2010). [BCH12a]: Israde-Alcántara et al. (2010 and refs. therein), Ferrusquía-Villafranca et al.2010). [RCH12 b]: Rosas-Elguera and Urrutia- Fucugauchi (1998), cited by Lucas (2008). [BCH12b]: Lucas 2008 and refs. therein), Ferrusquía-Villafranca et al. (2010). [RCH13]: Carranza-Castañeda et al. (2013). [BCH13]: Carranza-Castañeda et al. (2013). [RCH14]: 14a, Kowallis et al. (1998); 14b, Flynn et al. (2005). 14c. Israde-Alcántara and Garduño-Monroy (1999). [BCH14]: 14a, Carranza-Castañeda (2006 and refs. therein). [BCH15: Repenning (1962), Miller and Carranza (1984), Carranza-Castañeda (2006 and refs. therein).

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Plain; CeP, Central Plateau; TMVB, Trans-Mexican Volcanic Belt; the lower one being largely pyroclastic (red, moderately altered, thinly SMS, Sierra Madre del Sur; SMCh, Sierra Madre de Chiapas; and YPL, bedded, felsic, crystal-vitric, ash-fall and ash-flow tuffs). Both fossils Yucatán Platform. and zircon crystals for dating were taken from this part. The upper part is mainly epiclastic (fine to coarse-grained fluvial facies) and un- Other Considerations fossiliferous; Rubio-Cisneros and Lawton (2011) dated zircon crystals (a) the Pleistocene sites were not included. (b) The lithostratigraphic from this part (168-163 Ma). La Joya Fm. is a fluvial succession with a vertebrate-bearing units that have been numerically dated by magneto- basal conglomerate (Rubio-Cisneros and Lawton, 2011). stratigraphic methods, have not been included either because the paper The unit underlying the Huizachal Group does not crop out in the is solely focused on units dated by isotopic methods. (c) Appendix, area, but it is known that in northern Mexico, red bed sequences like Part A includes the geologic maps of the sites, Figures A1 through the Huizachal Group unconformably overlie crystalline basement rock A19. Appendix, Part B includes the taxonomic composition of the units of diverse ages (Proterozoic to Late Paleozoic) and attributes (cf. faunas and faunal assemblages, Tables B1 through B12. (d) The total Barboza-Gudiño et al., 2008 and references therein). The Huizachal number of sites investigated is 28 (they are reported as such in the text Group is overlain by the Late Jurassic Zuloaga Fm., a predominantly and listed in Table 1). However, these facts may lead to different total carbonate sequence that marks the onset of marine deposition in numbers: (d.1) two or more sites may lie so close to each other, that northeastern Mexico (Salvador, 1987). they could not be discriminated, that is why in Figure 1, only 25 sites Dating and regional significance. The ages reported by Fastovsky are plotted. (d.2) Several sites carry two sets of dated materials and et al. (1998, 2005) and Rubio-Cisneros and Lawton (2011) are moder- vertebrate faunas, that is why in Table 1, only 23 sites are numbered. ately different (see Table 1). Fastovsky et al. (2005) preferred 189±0.2 (d.3). Finally, only 27 sites are amenable to the North American Land Ma, earliest Pliensbachian [not Middle Toarcian, as they reported (cf. Mammal Age system of dating (Woodburne, 2004); the Jurassic and Gradstein et al., 2004)], as the maximal age of La Boca’s lower part. older faunas could not be independently dated/corroborated by current On the other hand, Rubio-Cisneros and Lawton (2011) convincingly magnetostratigraphic techniques. argued for slightly younger ages (184.2±1.2 Ma and 183±0.9 Ma, Late Pliensbachian). At any rate, the Huizachal Group registers an Early to Middle RESULTS AND DISCUSSION Jurassic volcanism (from the Nazas Volcanic Arc; Barboza-Gudiño et al., 2008) coeval to fluvial deposition occurring in an extensional Table 1 is a summary of the geographic, geologic and geochro- setting related to the dismembering of Pangea, and prior to the onset nologic information on the detected sites/localities where both iso- of the wide Late Jurassic marine transgression that extensively covered topically dated lithostratigraphic units and studied vertebrate fossils southern North America (including parts of Mexico; cf. Salvador, 1987). co-occur; they are treated below following a normal geochronologic La Boca local fauna is the earliest terrestrial vertebrate assemblage order. For each site, the information on the geological setting is pre- from Mexico, it includes mammal-like reptiles, early dinosaurs, ptero- sented and discussed first; its isotopic dating and vertebrate fos- saurs, early diapsids, sphenodonts and early mammals (Clark et al., sil assemblage is offered and discussed next, finishing with the 1994; Clark and Hopson, 1985; Fastovsky et al., 1995, 1998; Reynoso, regional significance of both the geologic and paleontologic data 1996), and closely resembles Early-Middle Jurassic faunas from North obtained. America (Kayenta Fm.), Eastern Asia (Lufeng Fm.) and South Africa (Clarence Fm.). The U-Pb dating results constrain the age to the late Jurassic Middle Jurassic, thus refining the biochronologic assessment. The widespread geographic distribution of the taxa/faunas involved indi- Cañón de Huizachal site cates that the Breaking up of Pangea-Vicarious Event separated taxa/ Tamaulipas State, Sierra Madre Oriental MP, Figure 1, Number 1; faunas once sharing the same area of distribution. Table 1, Number 1; Figures A1 and A2 Cretaceous The geology of this place is known for long time (Carrillo-Bravo, 1961 and references therein), however, detailed information on the El Rosario site Valle del Huizachal is scarce (Mixon, 1963a, 1936b; Fastovsky et al., Baja California State, Baja California Peninsula MP, Figure 1, 2005; Rubio-Cisneros and Lawton, 2011). The latter two contributions Number 2; Table 1, Number 2; Figure A3. will be briefly discussed due to their significant differences regarding the conceptions and cartographic boundaries of the units involved. This site is well known long ago (cf. Kilmer, 1963; Gastil et al., 1975; Both agree that the red bed sequence there belongs to the Huizachal Busby, 2004) however, published detailed geologic information (maps Group, which includes La Boca Formation (lower part) and La Joya included) is scarce (cf. Renne et al., 1991; Fulford and Busby-Spera, Formation (upper part). The first overlies a steeply bedded/banded 1993). The Cretaceous sedimentary cover in Baja California uncon- rhyolitic succession sparsely intercalated by basaltic flows/breccias formably rests on the Aptian-Albian Alisitos Fm. or on the Mesozoic and terrigenous clastic strata (shales to conglomerates). Fastovsky Batholith; this cover includes three units, readily observed in the area: et al. (2005) designated this succession Volcanic and Epiclastic Suite Bocana Roja Fm. (lower, continental, coarse-grained, unfossilifer- (VES), an informal unit (cf. NACSN, 1983, 2005) and interpreted it as ous), El Gallo Fm. (middle, continental to transitional, fine-clastic, recording a major angular unconformity due to tectonic activity prior vertebrate-fossiliferous) and El Rosario Fm. (upper, marine, carbonatic to Huizachal deposition. Alternatively, Rubio-Cisneros and Lawton and fine-siliciclastic). Late Cenozoic-Quaternary alluvial deposits (2011) interpreted it as a rhyolitic dome and adjacent deformation unconformably rest on this cover. zone developed in the host rock unit, an interpretation that we follow In turn, El Gallo Formation consists of three parts: La Escarpa in this work. member (lower, ~150 m thick, fluvial facies), El Disecado member La Boca Fm. is a ~54 m thick pyroclastic/epiclastic-volcarenitic (middle, ~1,150 m thick, fluvial and subtidal facies, vertebrate-fos- succession consisting of two texturally/compositionally different parts, siliferous, intercalated at various levels by rhyolitic, crystal-vitric tuff

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 329 Ferrusquía-Villafranca and Ruiz-González sheets) and El Castillo member (upper, continental, meso to coarse- and Stephens III, 1973; Ferrusquía-Villafranca, 1989, 2004, 2005) grained, it does not crop out in the area; Renne et al., 1991). includes reptiles (an iguanid), birds (a falconiform) and mammals Dating and regional significance. The 40Ar-39Ar ages obtained from [five orders (Condylarthra, Carnivora, Rodentia, Perissodactyla and the tuff sheets have a small spread (74.87±0.05 Ma to 73.59±0.09 Ma, Uncertain-Paleanodonta), six families, eight genera]. The condy- Renne et al., 1991; Table 1), placing this unit and its fauna in the Late larth Hyopsodus and perissidactyl Helaletes are characteristic Early Campanian; further, these authors also dated explosive volcanic activity Bridgerian taxa (cf. Robinson et al., 2004); largely on this basis this occurring concurrently with fluvial (and subsidiary tidal) deposition fauna is assigned to the Bridgerian NALMA (Robinson et al., 2004). within the rapidly subsiding Late Cretaceous El Rosario Basin, a small The lava flow age further corroborates this assignment. Finally, the portion of the Peninsular Ranges Forearc Basin (Renne et al., 1991). fauna shows an overall North American biogeographic affinity, but On the other hand, Busby (2004) in her regional tectonic study, con- endemism is apparent; some of the rodents (e.g. Marfilomys) show vincingly argues for regarding El Rosario as a forearc basin itself, and vague affinities with the early caviomorphs of South America (cf. so names it (Busby, 2004, fig. 3). Patterson and Wood, 1982). El Rosario l.f. (Lillegraven, 1972, 1976; Morris, 1972, 1973a, 1973b, 1981; Molnar, 1974) includes hadrosaurian and theropod dinosaurs Yoloméctal site as well as mammals (non-therian and therian), it resembles Judithian Oaxaca State, Sierra Madre del Sur MP, Figure 1, Number 4; faunas of western North America (e.g. that from the Judith River Fm.; Table 1, Number 4; Figure A5. Cifelli et al., 2004) and thus it was assigned to the Judithian NALMA (Cifelli et al., 2004); the isotopic dating corroborated/refined this. El Detailed geologic information for this place is lacking. The sum- Rosario l.f. is the southwestern most Cretaceous assemblage of North mary presented below draws from Ferrusquía-Villafranca (1976, America. adjacent northern area), López-Ticha (1985) and Santamaría-Díaz et al. (2008), the latter two are regional works that include this site. The Eocene oldest unit is the Middle Jurassic Tecocoyunca Group, unconformably overlain by the folded/faulted/uplifted Late Cretaceous Teposcolula Marfil site Limestone and Yucunama Marl, which form a north-south trending Guanajuato State, Central Plateau MP, Figure 1, Number 3; range. The Cenozoic sequence includes these units (from the bottom Table 1, Number 3; Figure A4. up): ?Yanhuitlán Fm. (Eocene, fluvio-lacustrine, fine-grained facies prevail; it is sparsely fossiliferous), Llano de Lobos Tuff (Oligocene, a This site is located in the Guanajuato Mining District, which holds thick pyroclastic sheet), Yucudaac Andesite (Oligocene, a thick flow the world class silver deposits of Guanajuato and, is geologically known stack), San Marcos Andesite (Oligocene, a less thick lava flow stack), long ago (cf. Edwards, 1955; Echegoyen-Sánchez et al., 1970, whose and Chilapa Fm. (Oligocene, intertongues the latter further north, it detailed lithostratigraphy is followed here). is largely lacustrine with abundant silicified limestone). The Esperanza Formation (a Late Mesozoic metamorphic complex Dating and regional significance. Near Sayultepec (~20 km south- with Late Cretaceous-Early Tertiary granitoid intrusions) constitutes east), a tuff sheet interbedded in the Yanhuitlán Fm. yielded a Pb α the oldest unit and is unconformably overlain by the Early Eocene age of 49.0±8.0 Ma (Ferrusquía-Villafranca, 1976). On the other hand, Guanajuato Conglomerate, a ~2,000 m thick fluvial sequence formed Martiny et al. (2000) reported a 40K-39Ar age of 40.5±1.7 Ma (Late by two members. The lower is ~1,300 m thick, largely consisting of Eocene) from an andesitic laccolith that intruded the Yanhuitlán Fm. fine grained, arkosic-volcarenitic sediments (overbank facies); it is little near Marcos Pérez (~10 km NE of the area), thereby yielding a minimal fossiliferous, and is also sparsely intercalated by andesitic lava flows. Late Eocene age for this formation. Later, Cerca et al. (2007) reported The upper member unconformably overlies the lower, it is a ~700 m a 40K-39Ar age of 43.2±1.2 Ma (Late Eocene) from the same laccolith. thick coarse-grained fluvial sequence (alluvial fan and debris flow Finally, Santamaría-Díaz et al. (2008, p. 500, tab., figs. 2-3) reported facies) expressed as deep red, clast to matrix supported conglomerate a 40K-39Ar age of 35.7±1.0 Ma (latest Eocene) for the Cañada María strata; it records rapid source-area uplift. Andesite, from a place situated ~4.5 km west of Tamazulapam (a town The Guanajuato Conglomerate is non-conformably overlain by located ~18 km north of Yolomécatl). The Cañada María Andesite is a thick volcanic succession that includes upward these units: Losero an informal unit that overlies the Yanhuitlán Fm., thus providing a Fm. (rhyolitic ash-flow tuffs, and tuffaceous sandstones), Bufa Rhyolite minimal age for the latter unit. (a ~30 m thick felsic ignimbrite sheet that yielded K-Ar ages of Summing up, in spite of their numerical differences, these four 37.5±3 Ma; Gross, 1975), Calderones Fm. (?Oligocene, a ~600 m thick, different ages (notwithstanding the large error of the first) place the largely pyroclastic pile), Cedro Fm. (?Pliocene, a ~50 m thick, largely Yanhuitlán Fm. in the Eocene. It remains to be proven whether the basaltic lava flow stack), Capulín Conglomerate (?Pliocene, a ~120 m so called Yanhuitlán Fm. at Sayultepec, Marcos Pérez, Santa Catarina thick, poorly consolidaded fluvial sequence) and Quaternary deposits Tayata and Yolomécatl sites actually is the same unit. Whichever the (alluvium, colluvium and soils) unconformably overlie the older units. case, such ages help to date the onset of the taphrogenic event subse- Dating and regional significance. A lower member lava flow yielded quent to the laramidic deformation in western Oaxaca, whereby the a 40K-40Ar age of 49.3±1.0 Ma (Aranda-Gómez and McDowell, 1998; Cretaceous units became folded, faulted and uplifted, and horst and Table 1), placing the Guanajuato Conglomerate in the Early Eocene, graben structurs developed. which is confirmed by the Bufa Rhyolite age. Previously though, Fries The Yolomécatl l.f. (Appendix Part B, Table B2; Jiménez-Hidalgo et al. (1955) reported Late Eocene-Early Oligocene vertebrates from et al., 2011) include five orders [Carnivora (one fam.), Creodonta this unit (now known to occur ~400 m above the dated flow), which (one fam.), Rodentia (two fam.), Perissodactyla (three fam.) and afford the first objective dating of the taphrogenic event immediately Artiodactyla (six fam.)] and 13 families; it has a Late Eocene outlook succeeding the Laramide Orogeny in Mexico, as well as the associated (?Duchesnian-?Chadronian), which is corroborated by the isotopic magmatism (both volcanic and intrusive). The geologic importance of ages discussed above. This fauna increases the Early Tertiary North this fact needs no further stressing. American fauna extent from central (Marfil l.f.) to southeastern Mexico The Marfil l.f. (Appendix Part B, Table B1; Fries et al., 1955; Black (Oaxaca).

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Early and Middle Miocene fluvio-lacustrine sequence formed by fine-grained subarkosic/tuf- faceous sandstone, siltstone and claystone set in thin/medium strata Tubutama site (overbank facies), intercalated by thick strata of volcarenitic conglom- Sonora State, Northwestern plains and sierras MP, Figure 1, erate (channel facies) and siliceous, fresh water limestone (lacustrine Number 5; Table 1, Number 5; Figure A6. facies). Thin sheets of silicic ash-flow and ash-fall tuffs are interbed- ding sedimentary strata at various levels; the one that crops out in and It is located in one of the basins that bear Tertiary fluvio-lacustrine around Etla constitutes the Etla Ignimbrite member, which commonly sequences associated to volcanic emplacements. Arriaga-Meléndez et dips 15 °NE. The vertebrate fossils (Suchilquitongo l.f.) were col- al. (1986) described the area, in the context of an economic geology lected from the fine-grained fluvial facies, ~80 m above this member (Borates) project. The pre-Cenozoic includes a Jurassic lithodem in- (Ferrusquía-Villafranca, 2003). The Suchilquitongo Fm. records fluvial truded by a Cretaceous granitoid, overlain by a Late Cretaceous clastic and lacustrine deposition in an actively subsiding basin. Quaternary marine succession, in turn covered by an up to ~1,120 m thick Cenozoic deposits and soils unconformably overlie the previous units. sequence consisting of six informal units (described upwards). Dating and regional significance. The Etla Ignimbrite member yield- Unit 1. A latest Eocene-earliest Oligocene, ~150 m thick stack ed 40K-40Ar ages of 20.3±0.4 Ma and 19.2±0.5 (Ferrusquía-Villafranca of andesitic and rhyolitic flows, pyroclastic breccias. Unit 2. A ~70 and McDowell, 1991; Table 1), which place the Suchilquitongo m thick, stratal pile of fine-grained arkosic sandstone and siltstone Formation in the Early Miocene; additionally these ages allow us to (lake facies) capped by a ~20 m thick, K-rich, palagonitized basaltic date the initial development of the Valle de Oaxaca Graben (Ferrusquía- andesite flow (vitric-textured by underwater emplacement). Unit 3. A Villafranca and Ruiz-González, 2007, 2011), because: (a) this is the first ~350 m thick, threefold stratal package: the lower part consists of red and only emplacement of a thick pyroclastic sheet in the northern arm to orange, fine-grained sediments [largely clay and silt (lake facies)], of this graben structure. (b) The pyroclastic sheets are confined to the intercalated by volcarenitic conglomerate lenses (fluvial, channel fa- graben (because none is present in the bounding horsts). Finally, these cies). The middle part consists of colemanite (CaB3O4(OH)3.H2O), isotopic ages also contribute to date the Late Tertiary volcanism in the gypsum, siltstone and fine grained sandstone strata (lake facies). The Sierra Madre del Sur M.P. (cf. Morán-Zenteno et al., 1999, 2000). The upper part largely consists of fresh water limestone. Unit 4. A ~ 200 m same applies for the Matatlán and Nejapa sites. thick stratal pile lithologically similar to Unit 3, but more frequently The Suchilquitongo l.f., (Appendix Part B, Table B3; Ferrusquía- includes limestone strata, and has little or no colemanite. Unit 5. A ~250 Villafranca, 1990b, 2003) includes three orders [Carnivora (one m thick stratal body formed by a red polymictic, matrix-supported, fam.), Perissodactyla (two fam.) and Artiodactyla (four fam.)], seven volcarentic conglomerate (debris flow and tallus facies). Unit 6. The families and 11 genera; its taxonomic makeup resembles that of the Baucarit Fm. unconformably overlies the previous units; it consists of Late Arikareean-Early Hemingfordian faunas of temperate North a Late Miocene basalt flow, covered by a ~100 m thick, volcarenitic, America (e.g. Harrison, Marsland and Sheep Creek; cf. Tedford et conglomeratic stratal body (fluvial facies). Finally, Quaternary alluvium al., 2004), accordingly its age falls within the Late Arikareean-Early deposits unconformably rest on this sequence. Hemingfordian NALMAs (Tedford et al., 2004). This assignment is Dating and regional significance. The palagonitized basalt flow consistent with the presented isotopic ages. Finally, the Suchilquitongo yielded a 40K-40Ar age of 22.3 Ma (Arriaga-Meléndez et al., 1986, who l.f. from Oaxaca stands midway between the chrono-correlative faunas cited as source an unpublished report for the Consejo de Recursos of North America (southern United States) and the Cucaracha l.f. from Minerales by Damon; Table 1), which places it in the earliest Miocene. the Panama Canal Zone (Whitmore and Stewart, 1965; MacFadden et Given that palagonitized basalts are not well suited for K-Ar dat- al., 2010) thus, corroborating the southward extension/continuity of ing, this age is questionable. Within Unit 3, ~80 m above the basalt the North America mammal fauna, during the Early Miocene. flow, we collected remains of the camel Stenomylus tubutammensis (Ferrusquía-Villafranca, 1990a). Stenomylus spans the Late Arikareean- Matatlán site Late Hemingfordian NALMA interval (Honey et al., 1998), however, Oaxaca State, Sierra Madre del Sur MP, Figure 1, Number 7; intrinsic evidence from S. tubutamensis led the senior author to prefer Table 1, Number 7; Figure A8. an Early Hemingfordian age (Ferrusquía-Villafranca, 1990a), which is consistent with the isotopic age. S. tubutamensis is one of the south- This Cenozoic sequence occupies the southeastern arm of the ernmost stenomyline records in North America. Geologically, these Valle de Oaxaca (Ferrusquía-Villafranca and Ruiz-González, 2007), isotopic and biochronologic ages date the beginning of basin develop- unconformably overlying folded and faulted carbonate sequences of ment in northwestern Sonora. Albian and Late Cretaceous ages. The Cenozoic includes the Matatlán Fm. (Ferrusquía-Villafranca, 2003, fig. 13.4), a ~300 m thick, fluvio- Suchilquitongo site lacustrine sequence consisting of four components: (a) fine-grained, Oaxaca State, Sierra Madre del Sur MP, Figure 1, Number 6; cross-bedded tuffaceous sandstone and clayey siltstone set in thin to Table 1, Number 6; Figure A7. medium strata (fluvial, largely overbank facies). (b) Clast-supported, pebble to cobble volcarenitic conglomerate set in thick strata (alluvial The local Cenozoic sequence is located in the northern arm of the fan and/or channel facies). (c) Laminar to thinly bedded clayey siltstone Valle de Oaxaca Graben (Ferrusquía-Villafranca and Ruiz-González, and silty claystone locally showing ripple marking (lacustrine facies). 2007), a Southeastern Mexico’s major structural feature, which is bound (d) Thin sheets of friable, felsic vitric ash-fall tuff interbedded at vari- to the west by the Late Proterozoic Oaxacan Complex and, to the east ous stratal levels (pyroclastic facies). by the Late Paleozoic-Mid Mesozoic Sierra de Juárez Metamorphic This unit registers fluvial and lacustrine deposition in a rapidly Complex (also named Sierra de Juárez Mylonitic Complex; SGM, subsiding basin with coeveal to intermittent pulses of silicic explosive 2000) and partly, by folded and faulted Cretaceous marine carbonate volcanism (Ferrusquía-Villafranca and Ruiz-González, 2007). The fine- units (SGM, 2007). grained fluvial facies bears vertebrates (the Matatlán l.f.). The Matatlán The Cenozoic includes andesitic lava flows at the base, and the Fm. intertongues and partly overlies the Mitla Tuff, a ~150–200 m thick Suchilquitongo Fm. (Wilson and Clabaugh, 1970), a ~750 m thick volcanic succession formed by welded, vitric crystal to crystal vitric

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 331 Ferrusquía-Villafranca and Ruiz-González rhyolitic to rhyodacitic ash-flow tuff and pyroclastic surges. Quaternary The Ixtapa l.f. (Appendix Part B, Table B5) is a small assem- deposits and soil crown the Cenozoic sequence. blage of vertebrates collected from overbank facies beds lying below Dating and regional significance. The Mitla Tuff yielded 40K-40Ar (~ 90 m) and above (~200 m) the dated tuff strata; it includes two ages of 16.0±0.8 Ma and 15.3±0.8 Ma (Ferrusquía-Villafranca and orders [Proboscidea (one fam.) and Perissodactyla (tw o fam.)], three McDowell, 1991; Table 1), thus placing it in the early Middle Miocene; families and three genera (Langenheim and Frost, 1963; Ferrusquía- that is, some 5 Ma younger than the Etla Ignimbrite of the Valle de Villafranca, 1990c, 2003; Bravo-Cuevas and Ferrusquía-Villafranca, Oaxaca Graben’s northern arm, which contains a largely similar sedi- 2008). This fauna’s makeup is comparable to that of the Early Barstovian mentary/pyroclastic fill. Further, this age dates the final development faunas of temperate North America (e.g. Pawnee Creek, Mascall and of this graben (Ferrusquía-Villafranca and Ruiz-González, 2007, 2011) Virgin Valley; cf. Tedford et al., 2004), hence it is assigned to the Early because (a) there are no volcanic successions covering the Mitla Tuff Barstovian NALMA (cf. Tedford et al., 2004), which is further corrobo- within or outside the graben. (b) There are no sedimentary deposits rated by the isotopic ages discussed above. The Ixtapa l.f. discloses that subsequent to such tuff and/or the Matatlán Fm., disclosing that the during this time, the North American mammal fauna uninterruptedly graben subsidence had ceased by this time (Middle Miocene), and with extended southwards down to central-western Chiapas. it the availability of accommodating space. The Matatlán l.f. (Appendix Part B, Table B4; Ferrusquía- Nejapa site Villafranca, 1990b, 2003; Bravo-Cuevas and Ferrusquía-Villafranca, Oaxaca State, Sierra Madre del Sur MP, Figure 1, Number 9; 2006, 2010) includes five orders [Carnivora (two fam.), Rodentia Table 1, Number 9; Figure A10. (one fam.), Proboscidea (one fam.), Perissodactyla (two fam.) and Artiodactyla (six fam.)], 12 families and 15 genera. Its taxonomic This local Cenozoic sequence unconformably overlies a ?Paleozoic composition is comparable to that of the Early Barstovian faunas of metamorphic complex and consists of the following units (Ferrusquía- temperate North America (e.g. Pawnee Creek, Deep River, Virgin Valley Villafranca, 2001), mentioned in stratigraphic order: and Mascall; cf. Tedford et al., 2004), thus it is assigned to the Early Limón Conglomerate (Eocene, ~900 m thick, of phyllarenitic and Barstovian NALMA (Tedford et al., 2004); this biochronologic dating calcilithitic composition). Yautepec Tuff and associated units (Middle is further corroborated by the isotopic age discussed above. Finally, Miocene, discordant over the Limón Cgl., a ~1,200 m thick, succes- the fact that all Matatlán taxa show North American biogeographic sion of felsic, largely welded, ash-flow tuffs, lapilli tuffs and surge affinities indicates that, at least during the Middle Miocene, the North emplacements; it partly intertongues and underlies El Camarón Fm. American mammal fauna extended uninterruptedly southward down and laterally, it also intertongues the Huitihuini Rhyolite. The latter is to Oaxaca. a stack of lava flows with marked fluidal texture; it is intruded by the San José de Gracia unit, which forms stocks, apophyses and dykes of Ixtapa site latitic to diabasic composition). Chiapas State, Sierra Madre de Chiapas MP, Figure 1, Number 8; El Camarón Fm. is a Middle Miocene, ~250 m thick fluvio- Table 1, Number 8; Figure A9. lacustrine sequence consisting of three components: (a) fine-grained, tuffaceous to volcarenitic sandstone, clayey siltstone and silty claystone The local Cenozoic sequence unconformably overlies Late set in thin to medium strata (overbank facies; vertebrate fossils were Cretaceous marine units; it includes a Paleocene-Middle Miocene, chiefly collected from it). (b) A pebble to cobble volcarenitic con- ~9,000 m thick, largely marine succession (Ferrusquía-Villafranca, glomerate set in thick strata (mainly channel facies). (c) Fine-grained, 1996), deposited in a “pull-apart” basin (Mandujano-Velázquez and parallel-bedded sandstone, clayey siltstone and silty claystone set in Keppie, 2009), placed in the Transcurrent-Fault Province of Chiapas laminar to thin strata (lacustrine/pond facies). This unit registers flu- (Sánchez-Montes de Oca et al., 1979); such basin is here interpreted vial/lacustrine deposition coeval to intense magmatic activity. Finally, as a fault-bend basin (cf. Busby and Ingersoll, 1995). Quaternary deposits (alluvium, colluvium) and soils unconformably The Ixtapa Fm. unconformably overlies the previous succession; it cover the Tertiary sequence. is a ~3,500 m thick fluvio-lacustrine and subordinately lagoonal stratal Dating and regional significance. The Yautepec Tuff yielded 40K-40Ar sequence consisting of five components: (a) fine-grained, tabular cross- ages of 15.82±0.37 Ma, 15.78±0.37 Ma and 14.96±0.8 Ma (Ferrusquía- bedded, tuffaceous to volcarentic sandstone, clayey siltstone and silty Villafranca, 2001; Table 1), thus placing this and its intertongued friable claystone (chiefly overbank facies). (b) Clast-supported, pebble units (El Camarón Fm. and Huithuini Rhyolite) in the early Middle to cobble calcilithitic conglomerate (mainly channel facies). (c) Very Miocene. These ages evidence that the Yautepec Tuff from the Oaxacan fine-grained tuffaceous to volcarenitic, parallel-bedded tuffaceous to Subisthmian region and the Mitla Tuff from the Valle de Oaxaca, some volcarenitic sandstone, clayey siltstone and silty claystone set in thin 51 km apart, are coetaneous. to laminar strata (lacustrine/pond facies). (d) Similarly made up strata Additionally, it should be noted that the coeval Ixtapa, Perros (from bearing marine and continental palynomorphs (coastal lagoon facies; the Isthmus of Tehuantepec; Ferrusquía-Villafranca, 1999), Yautepec Martínez-Hernández, 1992). (e) Felsic ash-flow and ash-fall tuffs set and Mitla Tuffs disclose widespread Middle Miocene (ca. 15 Ma) vol- in medium to thick strata, which make up about one third of this canic/magmatic activity in a ~380 km long arc-like “belt,” located at an unit. The Ixtapa Fm. records fluvial and subordinately coast lagoonal average distance of 95 km north from the present position of the Middle deposition in a rapidly subsiding basin, coetaneous with explosive American Trench/Cocos Plate subduction zone, and extending from silicic volcanic activity. This unit is overlain by the Punta de Llano central Oaxaca, over the Isthmian region to central-western Chiapas. Formation (a Middle Pleistocene, pyro-epiclastic succession) and by Such magmatic age-pattern does not support the east-ward Chortis other Quaternary deposits and soils. Block displacement model of Southeastern Mexico’s Cenozoic tectonic Dating and regional significance. The tuff part of the Ixtapa Fm. evolution (cf. Schaaf et al., 1995), nor the Cocos Plate leading edge yielded early-Middle Miocene 40K-40Ar ages of 16.02±0.53 Ma and model of Keppie and Morán-Zenteno (2005), thus paving the way for 15.02±0.35 Ma (Ferrusquía-Villafranca, 1996; Table 1). Such ages other alternative models (cf. Schulze et al., 2004; Nieto-Samaniego et date the structural deformation that generated the Transcurrent Fault al., 2006; Morán-Zenteno and Keppie, 2009; Silva-Romo and Mendoza- Province of Chiapas. Rosales, 2008).

332 RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx Isotope geochronology and vertebrate paleontology in México

The Nejapa fauna (Appendix Part B, Table B6; Ferrusquía- In La Purísima area, a Middle-Late Miocene unnamed, mesa- Villafranca, 1990b, 2003; Bravo-Cuevas and Ferrusquía-Villafranca, forming basalt flow stack that yielded 40K-40Ar ages between 14.6- and 2006, 2010) includes five orders [Carnivora (two fam.), Rodentia 7.0 Ma (Pallares et al., 2008), unconformably overlies the Comondú (one fam.), Proboscidea (one fam.), Perissodactyla (two fam.) and Fm. Such stack is in turn overlain by a ?Pliocene unnamed unit (a Artiodactyla (eight fam.)], 14 families and 20 genera. This fauna is com- hummocky relief-forming basalt flow stack). Quaternary basalt flows, parable to the Early Barstovian faunas of temperate North America (e.g. cinder cones and alluvial deposits unconformably overlie the older Pawnee Creek, Deep River, Virgin Valley and Mascall; cf. Tedford et al., units. 2004); thus it is assigned to the Early Barstovian NALMA (cf. Tedford Dating and regional significance. Tuff sheets from the Comondú Fm. et al., 2004), which is congruent with the isotopic ages discussed above. yielded Middle Miocene. 40K-40Ar ages of 13.0 and 14.5 Ma (McLean The Najapa fauna is more diverse than the Matatlán fauna, likewise it et al., 1987; Table 1). However, Umhoefer et al. (2001, p. 140) on the exclusively consists of North American taxa, a fact that confirms the basis of their own 40Ar-39Ar ages and a critical appraisal of previous southward extent of the North American land mammal fauna down ages, indicate that at Loreto (~80 km ESE from La Purísima), the Lower to Southern Mexico, at least during the Middle Miocene. clastic unit was laid down between ~21 and ~19 Ma (Early Miocene), Finally, it should be noted that the Miocene mammal fauna of but they also acknowledge that neither its lower nor upper boundaries Oaxaca includes lineages with both little derived and more derived are well constrained (due to the lack of suitable dating material at or taxa, which suggests that cladogenesis might have occurred there, i.e. close to them). southern tropical North America, and not only in temperate North However, the reported age differences of the Comondú “Formation/ America, as it is currently held; the Equini (Perissodactyla) and Group” at La Purísima and Loreto areas could adequately be explained Kiptoceratinae (Artiodactyla) are two examples. by these facts: (a) insufficient constraint of this unit’s lower and upper boundaries. (b) The diachroneity of this unit. (c) The Late Miocene La Purísima site U-Pb ages (19% of zircon crystals from a sample of the Comondú Baja California Sur State, Baja California Peninsula MP, Figure 1, “Formation/Group” collected in a locality placed 29 km west of La Paz Number 10; Table 1, Number 10; Figure A11. and ~310 km SSE from La Purísima, yielded ages as young as 9 Ma) reported by Fletcher et al. (2007, p. 1313, fig. 7). (d) The possibility Following McLean and Hausback (1984), and McLean et al. (1985, that the so called Comondú unit could not be the same rock body at 1987), the local Cenozoic succession includes the Late Oligocene San these three places. It follows that much detailed geologic work remains Gregorio Fm. (~70 m thick, diatomite, phosphatic shale/sandstone and to be done to correctly settle this issue. thin vitric, biotite-bearing tuff sheets; 40K-40Ar dated as of 27–23 Ma), At any rate, from a locality where the San Isidro and Comondú which is unconformably covered by the Middle Miocene, diachronous Formations intertongue, one of us recovered terrestrial and marine San Isidro/Comondú Fomations. The first (also spelled Ysidro) con- mammals (Ferrusquía-Villafranca, 1990a): Euoplocyon praedator sists of marine, light yellowish gray, fine-grained sandstone, siltstone (Carnivora, Canidae) and Desmostylus hesperus (Desmostylya, and shale, white coquina and a yellowish pebble conglomerate. It is Desmostylidae) respectively. Euplocyon’s biochronologic range spans very fossiliferous, its fauna is referred to the Vaqueros and Temblor the Late Hemingfordian-Early Barstovian (Tedford et al., 2004), but it Marine Stages, which in turn are nearly coetaneous with the Late is best known from the Early Barstovian Green Hills fauna of California Hemingfordian-Ealy Barstovian NALMAs (Barnes, 2002). (Woodburne et al., 1990). On the other hand, the marine mammal On the other hand, the Comondú unit has a long and involved Desmostylus is known in North America from the Early and Middle nomenclatorial history [from Beal (1948), who first used the term Miocene (McKenna and Bell, 1997), an interval roughly corresponding to the present (cf. Umhoefer et al., 2001; Fletcher et al., 2007)] con- to the Late Arikareean-Barstovian NALMAs (cf. Tedford et al., 2004). sequently, its conception, definition and usage varies enormously It follows that their co-occurrence would more probably fall in the from one author to another (see review by Umhoeffer et al., 2001). Late Hemingfordian-Early Barstovian time interval. However, the The latter authors upgraded the Comondú Formation to group rank, isotopic ages obtained from the Comondú tuff sheets and overlying their proposal, however, did not meet the requirements of the North mesa-basalts at La Purísima, allow us to constrain the interval to ca. American Stratigraphic Code (NACSN, 1983). Therefore, such change 14 Ma, which falls in the Early Barstovian NALMA (Tedford et al., of rank remains informal. Subsequent use [e.g. Fletcher et al. (2007, 2004) and La Purísima 1.f. is assigned to this age. Finally, it should p.1323) use Comondú Formation; fig.7] does not make it formal. be noted that this site is well suited to investigate direct correlation of Umhoefer et al. (2001) did not propose either the formations that marine and terrestrial stratal units and fossil assemblages in western their “Comondú Group” would include; instead, they propound these North America (Ferrusquía-Villafranca, 1990a), and on this regard three informal units: alone, it is very important. Lower clastic unit (200-300 m thick, coarse-grained, volcarenitic clastics sparsely intercalated by rhyolite tuff sheets and a few mafic lava Late Miocene flows; this unit has complex facies relations). Middle breccia and lava flow unit (largely dacitic to andesitic) and Upper lava flow and brec- Paso del Águila site cia unit (also largely dacitic to andesitic). The geologic interpretation San Luis Potosí State, Sierra Madre Oriental MP, Figure 1, of Umhoefer et al. (2001) is expressed in a regional map (1:500,000 Number 11; Table 1, Number 11; Figure A12. scale), which does not include the La Purísma area; therefore, such interpretation is not directly applicable here. Further, these authors The local Cenozoic succession unconformably overlies Late interpreted the Lower clastic unit as continental (fluvial and eolic), Cretaceous marine units; it consists of two Oligocene volcanic units in which is in contrast to other views that regarded it as largely marine the lower part and the San Nicolás Fm. (Ferrusquía-Villafranca et al., or transitional (cf. McLean and Hausback, 1984; McLean et al., 1985, 2015) that overlies them. The latter is a ~1,100 m thick, largely fluvial 1987). Certainly, in the La Purísima area our direct observations sequence that includes five components: (a) immature, calcilithitic, disclosed that the Comondú Formation includes both marine and frequently cross-bedded sandstone, clayey siltstone and silty claystone transitional facies (Ferrusquía-Villafranca, 1990a). set in thin to medium strata (channel and overbank facies). (b) Clast-

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 333 Ferrusquía-Villafranca and Ruiz-González supported, pebble to cobble, chiefly calcilithitic conglomerate set in The Chapala Fm. is a ~600 m thick sequence of thickly bedded medium to very thick strata (channel facies). (c) Very fine-grained, claystone, siltstone and partly diatomaceous shale, thinly bedded parallel-bedded calcilithitic sandstone, siltstone and claystone set in fresh water silty limestone (lacustrine facies); sparse thin interbeds thin strata (overbank facies), it is sparsely fossiliferous. (d) Subordinate of felsic ash-fall tuff (pyroclastic facies); and lesser amounts of cross- amounts of very fine-grained, parallel-bedded sandstone, clayey bedded volcarenitic sandstone and clast-supported conglomerate siltstone and claystone set in thin to very thin strata, interbedded by (fluvial facies); it commonly dips 20°–30°NE. (lithic description fresh water limestone (lacustrine/pond facies). (e) A few thin sheets updated by the authors). Quaternary alluvial deposits overlie this of felsic, vitric, ash-fall tuff, interbedded at various stratigraphic levels unit. (pyroclastic facies). This unit records largely fluvial -and subordinately Dating and regional significance. Israde-Alcántara et al. (2010, p. 88) lacustrine- deposition in a rapidly subsiding basin, coetaneous to reported a 40Ar-39Ar age of 7.0±0.3 Ma (Table 1) from a laccolith that intermittent silicic volcanic activity. The San Nicolás Formation is intruded the sedimentary sequence (i.e., the Chapala Formation), thus unconformably overlain by Quaternary deposits and soils. placing it at least in the Late Miocene; however, there are no vertebrate Dating and regional significance. The interbedded San Nicolás fossils known from this part of the sequence. These authors also tuff sheets yielded Late Miocene 40Ar-39Ar ages of 10.99±0.22 Ma and reported a 40Ar-39Ar age of 5.2±0.3 Ma (Table 1) of a tuff sheet associated 7.41±0.31 Ma (Ferrusquía-Villafranca et al., 2014; Table 1). These ages to diatom-bearing strata, which places the Chapala Formation in contribute to date a Late Tertiary, short-lived episode of continental the earliest Pliocene. Again, no vertebrates are known from this or deposition in a western graben of the Sierra Madre Oriental M.P., the associated beds in the sequence. On the other hand, such ages are only one known from this province so far. This example proves that concordant with the current interpretation of the tectonic evolution of the holistic study of sedimentary fills in other graben structures would the western TMVB (cf. Delgado-Granados, 1992, 1993; Rosas-Elguera improve the understanding of the Late Cenozoic geologic/tectonic et al., 1996; Michaud et al., 2000; Ferrari et al., 2000). evolution of the Sierra Madre Oriental. Finally, the presence of pre-Pleistocene mammals of Blancan age On the other hand, The Paso del Águila l.f. (Appendix Part B, in Chapala is known long ago (cf. Downs, 1958a, 1958b; Ferrusquía- Table B7; Ferrusquía-Villafranca et al., 2014) includes two orders Villafranca, 1978; Lucas, 2008), however, their precise stratigraphic [Perissodactyla (one fam.) and Artiodactyla (two fam.)], three families provenance is not known, nor have they been associated to isotopic and three genera of mammals, and a reptile (Chelonia). This fauna ages. The Pleistocene mammal fauna from this site is summarized and resembles the Late Clarendonian-Early Hemphillian faunas of temper- discussed in Ferrusquía-Villafranca et al., 2010. ate North America (e.g. McGehee Farm, Mixon, and Dove Springs; cf. Tedford et al., 2004). In fact, the perissodactyl Pliohippus potosinus Tepezalá area site displays a similar degree of cheek teeth development (in size and Zacatecas State, Sierra Madre Occidental MP, Figure 1, morphology) than Late Clarendonian-Early Hemphillian Pliohippus Number 13; Table 1, Number 13; Figure A14. species (cf. Kelly, 1998), hence leading us to assign this fauna to this Cofradía area site interval, an interpretation further corroborated by the isotopic ages Zacatecas State, Sierra Madre Occidental MP, Figure 1, discussed above. The lack of any South American taxon in this fauna Number 14; Table 1, Number 14; Figure A14. strongly suggests that the Panamian land connection was still not El Resbalón area site completed then. Zacatecas State, Sierras Madre Occidental MP, Figure 1, Number 15; Table 1, Number 15; Figure A14. Chapala site Jalisco State, Trans-Mexican Volcanic Belt MP (TMVB hereafter), These sites are located in the southern Sierra Madre Occidental Figure 1, Number 12; Table 1, Number 12; Figure A13. M.P., within the Juchipila Basin, one of the several NNE-SSE trending grabens or half grabens present there (cf. INEGI, 1974; SGM, 1991) This site is located in the Chapala Rift (first described by Clemens, developed in the Oligocene Upper Volcanic Complex (sensu McDowell 1963), in the western part of the TMVB, particularly on the northern and Keizer, 1977; McDowell and Clabaugh, 1979). Isotopic dating shore of Lake Chapala. Practically, there is no published detailed of tuff sheets of the horsts associated to the graben structures of the geologic information on the area, particularly for the sedimentary se- Juchipila Basin yielded ages between 25.9±2.5 Ma and 24.9±2.7 Ma quence that bears the vertebrate fossils. The exception is the geological (latest Oligocene, fission track method; Webber et al., 1994), which map of INEGI (1976), which only discriminates lithic units without would be the maximal age of graben development. a time frame. On the other hand, the tectonic and volcanologic lit- The sedimentary graben fill includes the Late Miocene-Early erature on this part of the TMBV is abundant (cf. Ferrari et al., 2012, Pliocene Juchipila Fm. (Lahiere, 1982; López, 1991; a unit never for- and references therein). The geologic summary given below, mally proposed), a ~90 m thick fluvio-lacustrine sequence formed by chiefly draws from Clemens (1963), INEGI (1976, 1988) and parallel-bedded, fresh water limestone and very fine-grained clastics SGM (1992). (lacustrine facies), interbedded by frequently cross-bedded volcarenitic The basal unit is a rhyolitic body, which seemingly yielded K-Ar sandstone and siltstone set in thin to medium bedded strata (mainly ages of 6.2 Ma and 3.4±0.2 Ma (Lucas, 2008, p. 40, fig. 7). However, overbank and channel facies; vertebrate fossils were collected from this the author does not state the source of the first age and attributes the facies). Thin sheets of felsic ash-fall tuff (pyroclastic facies) interbed second to Delgado-Granados et al. (1995), Rosas-Elguera et al. (1996) the sedimentary sequence at various levels. Finally, the Juchipila Fm. and Ferrari et al. (2000). Actually, the younger age is from a basalt is unconformably overlain by Quaternary gravel deposits. (Rosas-Elguera and Urrutia-Fucuguchi, 1998, tab. 1). The same authors Dating and regional significance. The tuff sheets in these sites also published a 6.26±1.21 Ma age from another basalt, that might be yielded U-Pb zircon ages ranging from 6.95±0.11 Ma (in Tepezalá, the source of the first age cited above. Carranza-Castañeda et al., 2013; Table 1), to 6.53±0.11 Ma (in La This basal unit is non-conformably overlain by the vertebrate- Cofradía, Carranza-Castañeda et al., 2013) and to 5.59±0.11 Ma (in bearing Chapala Fm., an informal unit proposed by Clemens (1963) El Resbalón, Carranza-Castañeda et al., 2013; Table 1), which gives without satisfying the pertinent requirements of ACSN (1961). latest Miocene-Early Pliocene ages for the Juchipila Fm. These ages

334 RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx Isotope geochronology and vertebrate paleontology in México also contribute to date Late Cenozoic pulses of volcanic activity and scale geological map (cf. INEGI, 1973; SGM, 2006). Finally, all these structural deformation in the southern Sierra Madre Occidental M.P., sequences record fluvial and/or lacustrine deposition taking place as well as continental depositions in their grabens/half grabens. coetaneously with pulses of explosive silicic volcanism. The local faunas of these sites constitute the Juchipila fauna Dating and regional significance. The tuff sheets yielded the follow- (Appendix Part B, Table B8), which includes five orders [Xenarthra (one ing isotopic ages: (a) 5.7±0.4 Ma (GTO2A site, Kowallis et al., 1998; fam.), Carnivora (one fam.), Proboscidea (one fam.), Perissodactyla fission track method; Table 1). (b) 5.50±0.05 Ma to 5.12±0.26 (Trapiche (two fam.) and Artiodactyla (four fam.)], nine families and 16 genera site, Carranza-Castañeda et al., 2013; U-Pb zircon method; Table 1). (Carranza-Castañeda et al., 2013). Its taxonomic content closely resem- (c) 4.989±0.16 Ma to 4.89±0.16 Ma (Tecolotlán site, Flynn et al., 2005; bles that of the Late Hemphillian faunas of temperate North America 40Ar-39Ar method). (d) 4.8±0.2 Ma (REO-GTO2C site, Kowallis et al., [e.g. Draw, Nebraska (Skinner et al., 1977), Wikieup, Arizona (Morgan 1998; fission track method; Table 1). Such ages place these sequences and White, 2005), Upper Bone Valley, Florida (Hulbert, 1987)], which in the Late to latest Miocene-earliest Pliocene; they also contribute to allows to assign it to the early Late Hemphillian (Hh2) NALMA (cf. date Late Cenozoic volcanism, faulting and continental deposition in Tedford et al., 2004). The above mentioned isotopic age corroborates the regions/areas of these sites. this interpretation. The combined mammalian assemblage of these local faunas Finally, in Mexico, the Juchipila fauna correlates with coeval faunas (Appendix Part B, Table B9) includes five orders [Xenarthra (one of Guanajuato, Nayarit and Jalisco (see below), which also include fam.), Carnivora (four fam.), Proboscidea (one fam.), Perissodactyla South American xenathrans, thus heralding the Great American (two fam.) and Artiodactyla (four fam.)], 13 families (all may not occur Biotic Interchange (GABI hereafter), a phenomenon known long ago in a given site) and 19 genera (Carranza-Castañeda, 2006; Carranza- (Scott, 1937; Ferrusquía-Villafranca, 1978), but much later named so Castañeda et al., 2013). Its taxonomic makeup is comparable to that (cf. Stehli and Webb, 1985). of Late Hemphillian faunas of temperate North America [e.g. Modesto Reservoir, California (Wagner, 1976), Edson Quarry, Kansas (Harrison, El Trapiche site 1983), Coffee Ranch (Dalquest, 1969)], therefore it is assigned to the Nayarit State, Sierra Madre Occidental MP, Figure 1, Number 16; latest Hemphillian NALMA (cf. Tedford et al., 2004). The isotopic ages Table 1, Number 16; Figure A15. cited above corroborate these finding. As in the faunas from Zacatecas, Rancho El Ocote (=REO)-GTO2A site; REO-GTO 2C the salient fact is the presence of South American immigrant taxa Both in: Guanajuato State, Central Plateau MP, Figure 1, (Megalonychidae), which evidence GABI’s initial phase. Finally, it Number 17; Table 1, Number 17; Figure A16. should be stressed that the San Miguel de Allende sequence also car- Tecolotlán site ries at its upper levels numerous Blancan mammal taxa, thus it is well Jalisco State, Trans-Mexican Volcanic Belt MP, Figure 1, suited to investigate Late Cenozoic biochronologic succession and Number 18; Table 1, Number 18; Figure A17. faunal turnover in central Mexico. To a lesser extent, this also applies to the Tecolotlán sequence. Published detailed geologic information for these sites/areas is scarce, and no lithostratigraphic units have been proposed. The brief Pliocene summary presented below draws from SGM (1991, 2006, 2014). These sites are located in the Late Cenozoic NNE-SSW elongate GTO 43 site basins set in graben structures developed in the southern part of the Guanajuato State, Central Plateau MP, Figure 1, Number 19; CeP (San Miguel de Allende Graben), the southwestern most part of the Table 1, Number 17; Figure A16. SMOc (El Trapiche Graben), and the western most part of the TMVB Rancho El Ocote, GTO 2D site (Tecolotlán Graben). It should be noted that under close examination, Guanajuato State, Central Plateau MP, Figure 1, Number 19; the Trapiche Graben shown by Carranza-Castañeda et al. (2013, fig. 2, Table 1, Number 17; Figure A16. seemingly a DEM -Digital Elevation Model- without explicit latitude Garbani, GTO 11 site and longitude coordinates) corresponds to a topographic depression, Guanajuato State, Central Plateau MP, Figure 1, Number 20; actually a valley with steep slopes and without topographic discontinui- Table 1, Number 20; Figure A16. ties (faults) that would characterize it as a graben structure. In contrast, La Pantera, GTO 12B site the San Miguel de Allende and Tecolotlán Grabens are clearly bounded Guanajuato State, Central Plateau MP, Figure 1, Number 21; by faults (Carranza-Castañeda et al., 2013, fig. 3; SGM, 2014). Table 1, Number 21; Figure A16. The sedimentary fill of these grabens and topographic depressions Estancia, GTO 5A site is formed by fluvio-lacustrine sequences a few dozens of meters thick, Guanajuato State, Central Plateau MP, Figure 1, Number 22; consisting of four components: (a) fine to coarse-grained, frequently Table 1, Number 22; Figure A16. cross-bedded, commonly volcarenitic sandstone, siltstone and claystone Rancho El Ocote, GTO 55 site set in thin to medium strata (fluvial facies). (b) Clast-supported, pebble Guanajuato State, Central Plateau MP, Figure 1, Number 17; to cobble conglomerate set in thick strata (fluvial, chiefly channel and Table 1, Number 17; Figure A16. fan facies). (c) Parallel-bedded, fine siltstone and silty claystone, and unfrequent calcareous claystone beds bearing ostracods and gastropods These six sites are located in the San Miguel de Allende Graben, set in thin strata (lacustrine facies). (d) Thin sheets of felsic ash-fall whose sedimentary fill was already described elsewhere (Rancho el tuffs that interbed the sequence at various levels (pyroclastic facies). Ocote and related sites above). It should be noted that these sequences are locally designated as Dating and regional significance. The tuff sheets associated to follows: (a) TnAr-Cgp unit (Tertiary Neogene sandstone-polymictic the fossiliferous strata yielded the following ages: (a) 4.747±0.032 conglomerate; SGM, 1999b) in the San Miguel de Allende area. (b) Ma (Rancho El Ocote, GTO 2D site, Flynn et al., 2005; 40Ar-39Ar Tpl.Cgp-Ar unit (Tertiary Pliocene-polymictic conglomerate and method; Table 1), 4.7±0.032 Ma (same site and reference as above) and sandstone; SGM, 2014) in the Tecolotlán area. (c) In the Trapiche area, 4.6±0.3 Ma (same site, Kowallis et al., 1998; fission track method; the local sequence is so small that it does not show up in the 1:50,000 Table 1). (b) 4.4±0.3 Ma (GTO 43 site, Kowallis et al., 1998; same

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 335 Ferrusquía-Villafranca and Ruiz-González method; Table 1). (c) 4.1±0.5 Ma [Garbani, GTO 11 site, same refer- On the other hand, the epiclastic part of this formation was ence and method as in (b); Table 1]. (d) 3.9±0.3 Ma [La Pantera, GTO described in more detail by Arellano-Gil et al. (2005) and according 12B site, same reference and method as in (b); Table 1]. (e) 3.32±0.02 to these authors, it is a 151.4 m thick sequence of volcarenitic [their Ma (Estancia, GTO 5A site, Flynn et al., 2005; 40Ar-39Ar method; “graywackes” (grauvacas)] conglomerate, sandstone (coarse to fine- Table 1). (f) 3.08±0.5 Ma (GTO 55 site, Kowallis et al., 1998; fission grained) and siltstone set in medium to thick strata, sparsely inter- track method; Table 1). These ages place the local sequences in the calated by tuff sheets. The conglomerate may form lenses or tabular late Early-Middle Pliocene and also contribute to date Late Cenozoic bodies that show cross bedding (channel facies). The siltstone may structural deformation and fluvio-lacustrine deposition in the southern show lamination and bear well preserved leaves, diatoms and ostracods part of the Central Plateau M.P. (lacustrine facies). The combined assemblage from these local faunas, herewith des- As for the Charo site, the published detailed geologic information ignated San Miguel fauna (Appendix Part B, Table B10; cf. Carranza- is also scarce. The following summary is taken from INEGI (1983), Castañeda, 2006 and references therein) includes: seven orders SGM (1995b), Silva-Mora (1995) and Israde-Alcántara and Garduño- [Xenarthra (one fam.), Lagomorpha (one fam.), Rodentia (two fam.), Monroy (1999). The site is located in north-east Michoacán, some Carnivores (two fam.), Proboscidea (one fam.), Perissodactyl (one 15 km ENE of Morelia. It is located in a small Late Cenozoic graben, fam.) and Artiodactyla (three fam.)], 11 families and 25 genera; its where a ~100 m thick, fluvio-lacustrine sequence was deposited; it taxonomic makeup is comparable to that of temperate North American non-conformably overlies the Miocene Mil Cumbres Complex (locally Blancan faunas [e.g. Vallecito Creek and Fish Creek, California (Downs its age ranges from 8±0.2 to 13.0 Ma; K-Ar method; Israde-Alcántara and White, 1968; Cassiliano, 1999) Buckeye Creek, Nevada (Kelly, and Garduño-Monroy, 1999). 1994) and Hagerman, Idaho (Mc Donald et al., 1996 and references The sedimentary sequence includes four components: (a) tabular therein)]. Hence, the San Miguel Fauna is assigned to the Early and cross-bedded volcarenitic sandstone and clayey siltstone set in thin to Middle Blancan NALMA (cf. Bell et al., 2004). The isotopic ages cited medium strata (channel and overbank facies, a few vertebrate fossils above corroborate the biochronologic age information. are present here). (b) Clast-supported, volcarenitic conglomerate forms The presence of two South American immigrant families lenses throughout the sequence (channel facies). (c) Parallel-bedded (Megalonychidae and Hydrochoeridae) in Guanajuato, evidences that siltstone, claystone and diatomite (lacustrine facies), which constitute GABI was then in full swing. On the other hand, on the basis of the nearly one half of the sequence. (d) A few interbedded thin felsic above cited ages, Flynn et al. (2005) argued that: (a) the Hemphillian/ ash-fall tuff sheets. Quaternary fine-grained clastic deposits that bear Blancan Boundary at Guanajuato should be placed at ~4.7–4.8 Pleistocene mammals, unconformably overlie the Pliocene sequence Ma. (b) The Guanajuato South American record predates for some (Carranza-Castañeda, 2006). 1.5–1.2 Ma GABI’s initial record in temperate North America. However, Dating and regional significance. The ash-fall tuff sheets in Amajac this can be questioned, because there are earlier Late Miocene records have yielded the following isotopic ages: (a) 4.591±0.007 Ma (Flynn et of megalonychids there (cf. Woodburne et al., 2006 and references al., 2005; 40Ar-39Ar method; Table 1). (b) 4.57±0.02 Ma [same reference therein). Other facts also suggests the need to revise GABI’s initiation, and method as in (a), Table 1]. (c) 4.2±0.3 Ma (Kowallis et al., 1998; such as the presence of Late Miocene North American mammals in fission track method; Table 1). On the other hand, in Charo only a sin- South America (e.g. the long known cyonasuan carnivores (Pascual, gle tuff sheet was independently dated twice: (a) 3.6±0.3 Ma (Kowallis 1972) and the seemingly earlier proboscidean record (Campbell et al., et al., 1998; fission track method). (b) 3.6 Ma (Israde-Alcántara and 2010). However, such kind of revision is beyond the scope of this paper. Garduño-Monroy, 1999; K-Ar method; Table 1). All these ages place the Finally, given that the Rancho El Ocote stratal succession at lower Amajac and Charo sequences in the Early-Middle Pliocene (although, levels also carries Hemphillian mammals, it is well suited for studying that of Amajac is slightly older), and correlate them with sequences of biochronologic succession and faunal turnover, as mentioned above. the San Miguel de Allende area, as discussed above. These ages also contribute to date Late Cenozoic volcanism and structural deformation Santa María Amajac site in the areas where the sites are located. Hidalgo State, Trans-Mexican Volcanic Belt MP, Figure 1, The combined Santa María Amajac-Charo mammalian assemblage Number 23; Table 1, Number 23; Figure A18. (Appendix Part B, Table B11; Repenning, 1962, and Carranza-Castañeda, Charo site 2006 and references therein) includes six orders [Lagomorpha (one Michoacán State, Trans-Mexican Volcanic Belt MP, Figure 1, fam.), Rodentia (two fam.), Carnivora (one fam.), Proboscidea (one Number 24; Table 1, Number 24; Figure A19. fam.), Perissodactyla (one fam.) and Artiodactyla (three fam.)], nine families and 14 genera; its taxonomic composition resembles that of The description of the first site is largely taken from Segerstrom the Blancan faunas from temperate North America [e.g. Hagerman, (1956, 1962), and SGM (1995a). The local sequence includes the Late Idaho (McDonald et al., 1996); Taunton and White Bluffs, Washington Tertiary volcanic Pachuca Group, which is unconformably overlain (Repenning et al., 1995)]. Therefore, this assemblage is assigned to the by the Atotonilco El Grande Formation, an informal unit proposed Blancan NALMA (cf. Bell et al., 2004). The isotopic ages cited above by Segestrom (1956) without fulfilling the then accepted requirements corroborate these findings. Finally, this combined assemblage is less (Ashley et al., 1933); such unit remains informal, because in spite of diverse than the San Miguel fauna, and as yet, it does not include South its subsequent use (cf. de Cserna et al., 1987; Arellano-Gil et al., 2005); American immigrant taxa. no one has ever formally proposed it since that time. The Atotonilco El Grande Fm. is a ~500–600 m thick volcanic Buenaventura site and epiclastic body that intertongues the Pliocene Navajas Rhyolite. Jalisco State, Trans-Mexican Volcanic Belt MP, Figure 1, The epiclastic part is a fluvio-lacustrine sequence, which besides the Number 25; Table 1, Number 25; Figure A17. expected channel and overbank deposits, also includes fresh water limestone (lacustrine facies), lignite and peat (palludal facies). It car- This site is located in the Tecolotlán Basin, which was already ries vertebrates, and is interbedded by thin rhyolitic ash-fall tuff sheets. described in site #18, thus we just add that the Hemphillian mammal- This unit is overlain by Quaternary deposits. bearing sequence is unconformably overlain by another fluvio-lacus-

336 RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx Isotope geochronology and vertebrate paleontology in México trine sequence carrying Blancan mammals. It is sparsely interbedded includes two chronofaunas: Clarendonian-Hemphillian (one record, by thin, felsic ash-fall tuff sheets. We are focusing here on the upper the first in Mexico) and Hemphillian (eight records, they carry some sequence. of the oldest registers of South American taxa in North America, thus Dating and regional significance. Samples from the tuff sheets heralding the full swing of the Great American Biotic Interchange). yielded a fission track age of 2.6±0.6 Ma (Kowallis et al., 1998; Table 1), The nine Pliocene sites (CeP, 6; TMVB, 3) record deposition associated thus placing it in the Late Pliocene. The Buenaventura l.f. (Appendix to tectonic and volcanic activity (taking place around 4.5-3.5 Ma), and Part B, Table B12) is small and includes only two orders [Perissodactyla their Blancan chronofauna includes numerous South American taxa (one fam.) and Artiodactyla (two fam.)], three families and three (which indicates that GABI was at its peak then. genera. It resemblances the Late Blancan faunas of temperate North 6. In spite of the large geographic spread (15 ° of latitude, spanning America (e.g. 111 Ranch, Arizona, Galusha et al., 1984), therefore, temperate and tropical zones/regions of diverse climate regimes we assign it to the Blancan NALMA (Bell et al., 2004). The above and biomic frameworks) and elapsed time (from Late Cretaceous mentioned fission track age, corroborates this interpretation. The to Pliocene) displayed by the 27 investigated sites that bear both possibility to investigate biochronologic succession in this basin was isotopically dated material and studied terrestrial vertebrate faunas, the already mentioned. North American Land Mammal Age System yielded biochronologic ages consistent with the isotopic ages. This cumulative evidence lends objective support to the empirical practice of assuming the idoneity/ SUMMARY AND CONCLUSIONS suitability of such system to adequately date the mammal faunas of Mexico, regardless the fact that it was developed from stratigraphic 1. We described/discussed the isotopic and paleontologic informa- successions of terrestrial mammal faunas that lived in temperate tion of 28 sites across the country, their distribution in space and time North America (largely southern Canada and the contiguous United is very uneven: BCP, one Cretaceous and one Miocene sites. NW, one States). This is indeed a major contribution to vertebrate paleontology Miocene site. SMOc, four Miocene sites. CeP, one Eocene and eight in this country. Miocene/Pliocene sites. SMOr, one Jurassic and one Miocene sites. 7. Concluding remarks. This brief review on the combined isotopic/ TMVB, two Miocene and three Pliocene sites. SMS, one Eocene and vertebrate paleontologic approach applied in Mexico during the last three Miocene sites. SMCh, one Miocene site. Patchiness/skewness fifty years, an effort developed through short term independent aside, the results are quite significant. projects, shows that it has nonetheless yielded valuable, albeit patchy 2. Mesozoic. The Pliensbachian Huizachal site (SMOr) is located geologic/paleontologic results. Clearly, the stage is set to undertake in the rift system that split central-eastern Pangea, records associated long-range, multidisciplinary/interinstitutional projects across the volcanism and bears Mexico’s oldest vertebrate fauna, which is fairly country, whose outcome could be a many-fold knowledge increase diverse and befittingly shows laurentic and gondwanic biogeographic that would qualitatively improve our understanding on the geologic/ affinities. The Rosario site (BCP) evidences Late Campanian fluvial biotic history and evolution of Mexico. (and subsidiarily tidal) deposition coetaneous to volcanism in the Peninsular Ranges Forearc Basin (or El Rosario Forearc Basin); its Judithian fauna shows western North American biogeographic af- ACKNOWLEGMENTS finities, as well as some degree of endemism (particularly among the dinosaurs). Much of the work on southeastern Mexico reported here could 3. Cenozoic. The Cenozoic sites lie in several graben structures and not have been possible without Grants from the CONACYT and NSF record episodes of deposition as well as tectonic and magmatic activ- to the senior author and to Fred McDowell (University of Texas at ity. Eocene-Early Miocene: The Marfil (CeP) and Yolomécatl (SMS) Austin) respectively during 1989-1990, to search for and investigate sites are located in basins associated to post-Laramide relaxation and sites containing actually/potentially vertebrate-fossiliferous sequences magmatism; their Bridgerian and ?Duchesnian/?Chadronian faunas and rocks suitable for isotopic dating. We thank Peter Schaaf, Teodoro evidence the southward extent of the North American Paleogene Hernández Treviño, Gabriela Solís Pichardo, Raymundo Martínez vertebrate fauna. Some taxa however, show strong endemism. The Serrano and Vianney Meza García their kind invitation to take part in Tubutama (NW) and Suchilquitongo (SMS) sites record deposition the “Simposio: 50±1σ años de Geocronología en México” to present a less associated to tectonic and magmatic activity (taking place by 20 Ma); known, but equally important facet of Isotopic Geochronology in this their faunas show North American biogeographic affinities and end- country; their encouragement to prepare this paper is most appreciated. emism seemingly related to isolation. The colleagues Luca Ferrari and Thierry Calmus kindly read the 4. Middle Miocene. The La Purísima (BCP), Matatlán (SMS), El first draft, Peter Schaaf and an anonymous reviewer read the second; Camarón (SMS) and Ixtapa (SMCh) sites record deposition related to all offered valuable suggestions to improve it. Certainly we duly tectonic and magmatic activity (occurring at ca. 15 Ma). The Valle de appreciate their generous effort. Last but not least, we thank the staff of Oaxaca Suchilquitongo and Matatlán sites disclose southward migra- the Biblioteca Conjunta de Ciencias de la Tierra, UNAM, for efficiently tion of such activity. Elsewhere in Southeastern Mexico, this process searching and retrieving information scattered in countless papers. generated a volcanic belt extending from the southeastern Valle de Oaxaca to northern Chiapas. Their faunas evidence the southern ex- tent of North America’s fauna at that time. Some taxa (e.g. Equini and APPENDIX. SUPPLEMENTARY MATERIAL Kyptoceratinae) though, show that their cladogenesis (partly at least) took place in tropical southern North America, rather than in temperate Part A. Includes the geologic maps of the sites, Figure A1 through “northern” North America, as it is currently thought. Figure A19. 5. Late Miocene and Pliocene. The Paso del Águila (SMOr), El Part B. Includes the taxonomic list of faunas and faunal assem- Resbalón, Cofradía, Tepezalá, El Trapiche (SMOc), Rancho El Ocote blages; Table B1 through Table B12. (CeP) and Tecolotlán (TMVB) sites record deposition coeval to tec- The files of this appendix can be found at the journal web site tonic and volcanic activity (ca. 9.5-5 Ma). Their mammal assemblages , in the table of contents of this issue.

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 337 Ferrusquía-Villafranca and Ruiz-González

REFERENCES State Of Zacatecas, Mexico, and its Biochronologic correlation with other Hemphillian faunas in Central Mexico: Contributions in Science, 521, ACSN (American Commission on Stratigraphic Nomenclature, 1961, Code 13-49. of Stratigraphic Nomenclature: American Association of Petroleum Carrillo-Bravo, J., 1961, Geología del anticlinorio de Huizachal-Peregrina al Geologists Bulletin, 45 (5), 645-665. NW de Ciudad Victoria, Tamaulipas: México, Boletín de la Asociación Aranda-Gómez, J.J., McDowell, F., 1998, Paleogene extension in the southern Mexicana de Geólogos Petroleros, 8, 1-98. Basin and Range Province of Mexico: Syndepositional tilting of Eocene Cassiliano, M.L., 1999, Biostratigraphy of Blancan and Irvingtonian mammals in red beds and Oligocene volcanic rocks in the Guanajuato Mining District: the Fish Creek-Vallecito Creek section, southern California, and a review International Geological Review, 40, 116-134. of the Blancan-Irvingtonian boundary: Journal of Vertebrate Paleontology, Arellano-Gil, J., Velasco-de León, P., Silva-Pineda, A., Salvador-Flores, R, Beltrán- 19, 169-186. Romero, F., 2005, Origen y características geológicas del Paleo-Lago de Cerca, M., Ferrari, L., López-Martínez, M., Martiny, B., Iriondo, A., 2007, Amajac, Hidalgo: Revista Mexicana de Ciencias Geológicas, 22, 199-211. Late Cretaceous shortening and early Tertiary shearing in the central Arriaga-Meléndez, H., Peña-Rocha, L., Gómez-Caballero, A., 1986, Resultados Sierra Madre del Sur, southern Mexico: Insights into the evolution of the de la evaluación de depósitos de boratos del área Tubutama, Sonora: Caribbean–North American plate interaction: Tectonics, 26, TC3007. GEOMIMET, 141, XIII Época, Mayo-Junio, 41-60. Cifelli, R.L., Eberly, J., Lofgren, D.L., Lillegraven, J.A., Clemens, W.A., 2004, Ashley, G.H., Cheney, M.G., Gould, J.J., Gallaway, C.N., Hares, C.J., Howell, Mammalian Biochronology of the Lates in Cretaceous. Late Cretaceous B.F., Levorsen, A.I., Miser, H.D., Moore, R.C., Reeside, J.B., Jr., Rubey, and Cenozoic Mammals of North America, in Woodburne, M.O., (ed.), W.W., Station, T.W., Stone, G.W., Twenhofel, W.H., 1933, Classification Late Cretaceous and Cenozoic Mammals of North America: New York, and nomenclature of rocks units: Geological Society of America Bulletin, Columbia University Press, 21-42. 44, 423-459. Clark, J.M., Hopson, J.A., 1985, Distinctive mammal-like reptile from Mexico and Barboza-Gudiño, J.R., Orozco-Esquivel, M.T., Gómez-Anguiano, M., Zavala- its bearing in the phylogeny of the Tritilodontidae: Nature, 315, 398-400. Monsiváis, A., 2008, The Early Mesozoic volcanic arc of western North Clark, J.M., Montellano, M., Hopson, J.A., Hernandez, R., Fastovsky, D.E., America in northeastern Mexico: Journal South American Earth Sciences, 1994, An Early or Middle Jurassic tetrapod assemblage from the La Boca 25, 49-63. formation, northeastern Mexico, in Fraser, N.C., Suhadoes, H.D., (eds.), Barnes, L.G., 2002, Evolutionary history of the fossil marine mammals of In the Shadow of the Dinosaurs: Cambridge, Cambridge University Press, Mexico, in Montellano-Ballesteros, M., Arroyo-Cabrales, J. (eds.), Avances 294-302. en los estudios paleomastozoológicos: México, Instituto Nacional de Clemens, T., 1963, Pleistocene history of Lake Chapala, Jalisco, México, in Antropología e Historia, Colección Científica, Serie Arqueología, 125-226. Clemens, T., Stevenson, R.E., Halmos D.E., (eds.), Essays in Marine Beal, C.H., 1948, Reconnaissance of the geology and oil possibilities of Baja Geology in honor of K.O. Emery: Los Angeles, University of Southern California: Geological Society of America, Memoir 31, 138. California Press, 35-49. Bell, C.J., Lundelius Jr., E.L., Barnosky, A.D., Graham, R.W., Lindsay, E.H., Ruez Collinson, J.D., 1996, Sedimentary Environments: Processes, Facies and Jr., D.R., Semken Jr., H.A., Webb, S.D., Zakrzewski, R.J., 2004, The Blancan, Stratigraphy: Alluvial sediments: Blackwell Publishing Company, 37-82. Irvingtonian, and Rancholabrean mammal ages, in Woodburne, M.O. (ed.), Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (CONABIO), Late Cretaceous and Cenozoic Mammals of North America: New York, 2003, Mosaico 2002 imágenes Modis sin nubes, satélite Terra, bandas 1,4,3 Columbia University Press, 232-314. (RGB), resolución espacial 250 metros, sobre un modelo digital de terreno: Black, C.C., Stephens III, J.J., 1973, Rodents from the Paleogene of Guanajuato, México, 1 imagen. Mexico: Texas Tech University Museum, Occasional Papers, 14, 1-10. Dalquest, W.W., 1969, Pliocene carnivores of the Coffee Ranch: Texas, Bulletin Boggs, S.Jr., 1995, Petrology of sedimentary rocks: Cambridge, Cambridge of the Texas Memorial Museum, 15, 1-43. University Press, 600 pp. De Cserna, Z., de la Fuente-Dutch, M., Palacios-Nieto, M., Triat, L., Mitre- Bonhomme, M., Thuizat, R., Pinault, Y., Clauer, N., Wedling, R., Wincler, R., Salazar, L.M., Mota-Palomino, R., 1987, Estructura geológica, gravimetría, 1975, Methode de datation Potassium-Argon. Appareillage et technique: sismicidad y relaciones neotectónicas regionales de la Cuenca de México: France, Universidade Strasbourg, Institute Geologie, Technical Report, México, Universidad Nacional Autónoma de México, Instituto de Geología, 95 pp. Boletín 104, 71 pp. (Includes 4 plates, Pl. 1 is a geologic map scale Bravo-Cuevas, V.M., Ferrusquía-Villafranca, I., 2006, Merychippus (Mammalia, 1:250,000). Perissodactyla, Equidae) from the Middle Miocene of Oaxaca State, Delgado-Granados, H., 1992(1993), Tectonics of the Chapala region, México, in Southeastern Mexico: Geobios, 39(6), 771-784. Aoki, K.I., (ed.), Subduction, Volcanism and Tectonics of Western Mexican Bravo-Cuevas, V.M., Ferrusquía-Villafranca, I., 2008, Cormohipparion Volcanic Belt: Sendai, Japan, Report of the Monbusho Grant for the joint (Mammalia, Perissodactyla, Equidae) from the Middle Miocene of the project Japan-Mexico Co-operative, 194-212. State of Oaxaca, Southeastern Mexico: Journal of Vertebrate Paleontology, Delgado-Granados, H., Urrutia-Fucugauchi, J., Hasenaka, T., Ban, M., 1995, 28(1), 243-250. Southwestward volcanic migration in the western Trans-Mexican Volcanic Bravo-Cuevas, V.M., Ferrusquía-Villafranca, I., 2010, The oldest record of Equini Belt During the last 2 Ma: Geofísica Internacional, 34(3), 341-352. (Mammalia: Equidae) from Mexico: México, Revista Mexicana de Ciencias Downs, T., 1958a, Fossil vertebrates from Lago de Chapala, Jalisco, Mexico: 20th Geológicas, 27(3), 593-602. International Geological Congress: México, Section 7, 75-77. Busby, C., 2004, Continental growth at convergent margins facing large ocean Downs, T., 1958b, From the bottom of the lake: Los Angeles, Country Museum basins: A case study from Mesozoic convergent-margin basin of Baja Quarterly, 14(4), 8-9. California: Tectonophysics, 392, 241-277. Downs, T., White, J., 1968, A vertebrate faunal succession in superposed Busby, C.J., Ingersoll, R.V. (eds.), 1995, Tectonics of sedimentary basins: London, sediments from late Pliocene to middle Pleistocene in California, in Blackwell Science, 579 pp. Tejkal, J., (ed.), Proceedings of Section 10: Tertiary/Quaternary boundary: Campbell Jr., K., Prothero, D., Romero-Pittman, L., Hertel, F., Rivera, N., 2010, Czechoslovakia, Prague, International Geological Congress report of the Amazonian magnetostratigraphy: Dating the first pulse of the Great twenty-third session, Academia, 41-47. American Faunal Interchange: Journal of South American Earth Sciences, Echegoyen-Sánchez, J., Romero-Martínez, S., Velázquez-Silva, S., 1970, 29(3), 619-626. Geología y Yacimientos minerales de la parte central del Distrito Minero Carranza-Castañeda, O., 2006, Late Tertiary fossil localities in Central Mexico de Guanajuato: México, Consejo de Recursos Naturales no Renovables, between 19°-23° N, in Carranza-Castañeda, O., Lindsay, E.H., (eds.), Boletín, 75, 35. Advances in Late Tertiary Vertebrate Paleontology in Mexico and the Great Edwards, J.D., 1955, Studies of some early Tertiary red conglomerates of central American Biotic Interchange: México, Universidad Nacional Autónoma Mexico: United States Geologic Survey, Professional Paper 246-H, 153-183. de México, Instituto de Geología and Centro de Geociencias, Publicación Fastovsky, D.E., Clark, J.M., Strater, N.H., Montellano, M., Hernandez, R.R., Especial, 4, 45-60. Hopson, J.A., 1995, Depositional environments of a Middle Jurassic Carranza-Castañeda, O., Aranda-Gómez, J.J., Wang, X., Iriondo, A., 2013, The vertebrate assemblage, Huizachal Canyon, México: Journal of Vertebrate Early-Late Hemphillian (Hh2) Faunal Assemblage From Juchipila Basin, Paleontology, 15, 561-575.

338 RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx Isotope geochronology and vertebrate paleontology in México

Fastovsky, D.E., Bowring, S., Hermes, O., 1998, Radiometric age dates for the areas in Southeastern Mexico- Its bearing in understanding regional basin La Boca vertebrate assemblage (Late Early Jurassic), Huizachal Canyon, development there: México, Universidad Nacional Autónoma de México, Tamaulipas, Mexico: México, Universidad Autónoma del Estado de Instituto de Geología, Memoria, Convención sobre la evolución geológica Hidalgo, Instituto de Investigación en Ciencias de la Tierra, Publicación de México, Pachuca, Hidalgo, 45-50. Especial 1, Paleontología de Vertebrados, 15-17. Ferrusquía-Villafranca, I., Ruiz-González, J., 2007, Sedimentary environments Fastovsky, D.E., Hermes, O.D., Strater, N.H., Bowring, S.A., Clark, J.M., and tectonic control of the Valle de Oaxaca Graben Miocene continental Montellano, M., Hernández, R.R., 2005, Pre-Late Jurassic, fossil bearing succession, Southeastern Mexico: Geological Society of America, Annual volcanic and sedimentary red beds of Huizachal Canyon, Tamaulipas, Meeting and Exposition, Abstracts with Programs, 39(6), 338. Mexico, in Anderson T.H., Nourse, J.A., McKee, J.W., Steiner, M.B., (eds.), Ferrusquía-Villafranca, I., Ruiz-González, J., 2011, Modelo evolutivo tectono- The Mojave-Sonora Megashear hypothesis: Development, assessment and sedimentario del Graben Valle de Oaxaca: Integración parsimoniosa de la alternatives: Geological Society of America, Special Paper, 393, 401–426. información geológica y paleontológica disponible: México, Universidad Ferrari, L., Paquaré, G., Venegas-Salgado, S., Romero-Rios, F., 2000, Geology of Nacional Autónoma de México, Instituto de Geología, Dr. Zoltan de the western Mexican volcanic belt and adjacent Sierra Madre Occidental Cserna: Sesenta años geologizando México, Libro de Resúmenes, 165-171. and Jalisco block: Geological Society of American, Special Paper, 334, Ferrusquía-Villafranca, I., Jiménez-Hidalgo, E., Bravo-Cuevas, V. M., Montaño- 65-83. Martínez, I., 2006, Adición a la Fauna Suchilquitongo, Hemingfordiano Ferrari, L., Orozco-Esquivel. T., Manea, V., Manea, M., 2012, The dynamic de Oaxaca, Sureste Mexicano y su significación paleobiológica: Memoria, history of the Trans-Mexican Volcanic Belt and the Mexico subduction X Congreso Nacional de Paleontología, Cd. México, Nov. 21-25, Libr. zone: Tectonophysics, 522-523, 122-149. Guía Exc. Tepexi de Rodríguez, Pue., Universidad Nacional Autónoma Ferrusquía-Villafranca, I., 1971, Geology of the Tamazulapam-Teposcolula- de México, Instituto de Geología, Publicación Especial, 36. Yanhuitlan Area, Mixteca Alta, Estado de Oaxaca, Mexico: U.S.A., Ferrusquía-Villafranca, I., Arroyo-Cabrales, J., Martínez Hernández, E., Gama- University of Texas at Austin, Ph.D. Dissertation, 247 p. Castro, J., Ruiz-González, J., Polaco, O.J., Johnson, E., 2010, Pleistocene Ferrusquía-Villafranca, I., 1976, Estudios Geológico-Paleontológicos en la Mammals of Mexico: A Critical Review of Regional Chronofaunas, Región Mixteca Pt. 1: Geología del Area Tamazulapam-Teposcolula- Biogeographic Provinciality and Climate Change Response: Quaternary Yanhutlán, Mixteca Alta, Estado de Oaxaca, México: México, Universidad International, 217, 53-104. Nacional Autónoma de México, Instituto de Geología, Boletín, 97, 160 p., Ferrusquía-Villafranca, I., Ruiz-González, J.E., Martínez-Hernández, E., Torres- 27 Tablas, 9 Figs., 17 Láms. Hernández, J.R., Woolrich-Piña, G., 2014, A new Miocene local fauna from Ferrusquía-Villafranca, I. (ed.), 1978, Conexiones terrestres entre Norte the Sierra Madre Oriental at San Luis Potosí, central-east Mexico, and its y Sudamérica: Simposio Interdisciplinario sobre Paleogeografía paleontologic significance: Geobios, 47, 199-220. Mesoamericana: Universidad Nacional Autónoma de México, Instituto Ferrusquía-Villafranca, I., Ruiz-González, J.E., Torres-Hernández, J.R., Martínez- de Geología, Boletín, 101 p. Hernández, E., 2015, A new Miocene Formation from The Peotillos- Ferrusquía-Villafranca, I., 1989, A new rodent genus from Central México and Tolentino Graben Fill, Western Sierra Madre Oriental at San Luis Potosí, its bearing on the origin of the Cavimorpha, in Black, C.C., Dawson, M.R., Mexico: Part 1, Geology: Boletín de la Sociedad Geológica Mexicana, in (eds.), Paper on fossil rodents in honor of Albert Elmer Wood: Los Angeles, press. Natural History Museum, Science Series, 33, 91-117. Fisher, R.V., Schmincke, H.U., 1984, Pyroclastic Rocks: Berlin, Springer-Verlag, Ferrusquía-Villafranca, I., 1990a, Biostratigraphy of the Mexican continental 472 pp. Miocene, Part I, Introduction and the Northwestern and Central faunas: Fletcher, J.M., Grove, M., Kimbrough, D., Lovera, O., Geherels, G.E., 2007, Ridge- México, Universidad Nacional Autónoma de México, Instituto de Geología, trench interactions and the Neogene tectonic evolution of the Magdalena Paleontología Mexicana, 56, 8-53. Shelf and southern Gulf of California: Insights from detrital zircon U-Pb Ferrusquía-Villafranca, I., 1990b, Biostratigraphy of the Mexican continental ages from the Magdalena Fan and adjacent areas: Gelogical Society of Miocene: Part II, The Southeastern (Oaxacan) faunas: México, Universidad America Bulletin, 119, 1313-1336. Nacional Autónoma de México, Instituto de Geología, Paleontología Flynn, J.J., Kowallis, B.J., Nuñez, C., Carranza-Castañeda, O., Miller. W.E., Mexicana, 56, 57-109. Swisher, C.C.III, Lindsay, E., 2005, Geochronology of Hemphillian-Blancan Ferrusquía-Villafranca, I., 1990c, Biostratigraphy of the Mexican continental aged strata, Guanajuato, Mexico, and implications for timing of the Great Miocene: Part III, The Southeasternmost (Chiapasan) fauna and concluding American Biotic Interchange: Journal of Geology, 112, 287-307. remarks on the discussed vertebrate record: México, Universidad Nacional Folk, R.L., 1974, Petrology of sedimentary rocks: Austin, Hemphill, 182 pp. Autónoma de México, Instituto de Geología, Paleontología Mexicana, Fries, C.Jr., Hibbard, C.W., Dunkle, D.H., 1955, Early Cenozoic vertebrates in the 56, 113-149. Red Conglomerate at Guanajuato Mexico: Washington, D,C., Smithsonian Ferrusquía-Villafranca, I., 1996, Contribución al Conocimiento Geológico de Miscellaneous Collections, 123, 1-25. Chiapas: El Área Ixtapa-Soyaló: México, Universidad Nacional Autónoma Fulford, M.M., Busby-Spera, C., 1993, Tectonic controls on non-marine de México, Instituto de Geología, Boletín, 110, 130 p. sedimentation in a Cretaceous fore-arc basin, Baja California, Mexico, Ferrusquía-Villafranca, I., 1999, Contribución al conocimiento Geológico in Frostick, L.E., Steel, R.J., (eds.), Tectonic controls and signatures in de Oaxaca: El Área Laollaga-Lachivizá: México, Universidad Nacional sedimentary succession: International Association of Sedimentologists, Autónoma de México, Instituto de Geología, Boletín, 111, 110 p. Special Publication, 20, 301-333. Ferrusquía-Villafranca, I., 2001, Contribución al conocimiento geológico del Galusha, T., Johnson, N.M., Lindsay, E.H., Opdyke, N.D., Tedford, R.H., 1984, Estado de Oaxaca, México-El Área Nejapa de Madero: México, Universidad Biostratigraphy and magnetostratigraphy, late Pliocene rocks, 111 Ranch, Nacional Autónoma de México, Instituto de Geología, Boletín, 111, 1-100 Arizona: Geological Society of America, Bulletin, 95, 714-722. pp. Gastil, G., Philips, R.P., Allison, E.C., 1975, Reconnaiscence geology of Baja Ferrusquía-Villafranca, I., 2003, Mexico's Middle Miocene mammalian California Norte: Geological Society of America, Memoir 14, 170 pp. assemblages: An overview: American Museum of Natural History, Bulletin, Gehrels, G.E., Valencia, V.A., Ruiz, J., 2008, Enhanced precision, accuracy, 279, 321-347. efficiency and spatial resolution of U-Pb ages by laser ablation- Ferrusquía-Villafranca, I., 2004, A new Eocene palaeanodont from Central multicollector-inductively coupled plasma-mass spectrometry: Mexico: Society of Vertebrebrate Paleontology, 64th Annual Meeting, Geochemistry Geophysics Geosystems, 9(3), 1-13. Madison, WIS., Abstracts of Papers, Journal of Vertebrate Paleontology, Gradstein, F.M., Ogg, J.G., Smith, A.G., 2004, Chronostratigraphy; linking time 33(3), 57A. and rock, in Gradstein, F.M., Ogg, J.G., Smith, A.G., (eds.), A Geological Ferrusquía-Villafranca, I., 2005, The Marfil Local Fauna, Bridgerian of Time Scale 2004: Cambridge, Cambridge University Press, 20-46. Guanajuato, Central Mexico: Review and Significance. A Progress Report Gross, W.H., 1975, New ore discover and source of silver-gold veins, Guanajuato, on the Southernmost Tetrapod Assemblage of North America: Society of Mexico: Economic Geology, 20, 701-704. Vertebrate Paleontology, 65th, Annual Meeting, Phoenix, AZ., Abstracts Harrison, J.A., 1983, The Carnivora of the Edson local fauna (late Hemphillian), of Papers, Journal of Vertebrate Paleontology, 24(3), 56A. Kansas: Smithsonian Contribution to Paleobiology, 54, 1-28. Ferrusquía-Villafranca, I., McDowell, F., 1991, The Cenozoic sequence of selected Honey, J.G., Harrison, J.A., Prothero, D.R., Stevens, M.S., 1998, Camelidae, in

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 339 Ferrusquía-Villafranca and Ruiz-González

Janis, M.C., Scott K.M., Jacobs, L.L., (eds.), Evolution of Tertiary Mammals Lucas S.G., 2008, Late Cenozoic fossil mammals from the Chapala rift basin, of North America, Volume 1, Terrestrial carnivores, ungulates and Jalisco, Mexico. Neogene Mammals: New Mexico, Museum of Natural ungulatelike mammals: Cambridge, Cambridge University Press, 439-462. History and Science Bulletin, 44, 39-49. Hulbert, R.C., 1987, Late Neogene Neohipparion (Mammalia, Equidae) from MacFadden, B.J., Kirby, M.X., Rincon, A., Montes, C., Moron, S., Strong, N., the Gulf Coastal Plain of Florida and Texas: Journal of Paleontology, 61, Jaramillo, C., 2010, Extinct peccary Cynorca occidentale (Tayassuidae, 809-830. Tayassuinae) from the Miocene of Panama and correlations to North INEGI (Instituto Nacional de Estadística, Geografía e Informática), 1973, Carta America: Journal of Paleontology, 84(2), 288-298. Geológica Yesca F13-D33, escala 1:50,000: México, D.F., Secretaría de la Mandujano-Velázquez, J.J., Keppie, J.D., 2009, Middle Miocene Chiapas fold and Presidencia, Comisión de estudios del Territorio Nacional, 1 mapa. thrust belt of Mexico: a result of collision of the Tehuantepec Transform/ INEGI (Instituto Nacional de Estadística, Geografía e Informática), 1974, Carta Ridge with the Middle America Trench: London, Geological Society, Geológica Juchipila F13-D36, escala 1:50,000: México, D.F., Secretaria de Special Publications, 327, 55-69. la Presidencia, Comisión de Estudios del Territorio Nacional, 1 mapa. Martínez-Hernández, E., 1992, Caracterización ambiental del Terciario de la INEGI (Instituto Nacional de Estadística, Geografía e Informática), 1976, Carta región de Ixtapa, Estado de Chiapas un enfoque palinoestratigráfico: Geológica Chapala F13-D76, escala 1:50,000: México, D.F., Secretaria de México, Universidad Nacional Autónoma de México, Revista del Instituto la Presidencia, Comisión de Estudios del Territorio Nacional, 1 mapa. de Geología, 10(1), 54-64. INEGI (Instituto Nacional de Estadística, Geografía e Informática) 1983, Carta Martiny, B., Martínez-Serrano, R.G., Morán-Zenteno, D.J., Macías-Romo, C., Geológica Morelia E14-1, escala 1:250,000: México, D.F., Secretaria de Ayuso, R.A., 2000, Stratigraphy, geochemistry and tectonic significance Programación y Presupuesto, Dirección General de Estudios del Territorio of the Oligocene magmatic rocks of western Oaxaca, southern Mexico: Nacional, 1 mapa. Tectonophysics, 318, 71-98. INEGI (Instituto Nacional de Estadística, Geografía e Informática), 1988, Carta McDonald, G.H., Link, P.K., Lee D.E., 1996, Pleistocene caribou (Rangifer Geológica Guadalajara F13-12, escala 1:250,000: México, D.F., Secretaria de tarandus) in the eastern United States: New records and range extensions, in Programación y Presupuesto, Dirección General de Estudios del Territorio Stewart, K.M., Seymour, K.L., (ed.), Palaeoecology and palaeoenvironments Nacional, 1 mapa. of late Cenozoic mammals: Tributes to the career of C.S. (Rufus) Churcher: Israde-Alcántara, I., Garduño-Monroy, V.H., 1999, Lacustrine record in a Toronto, University of Toronto Press, 406-430. volcanic intra-arc setting: The evolution of the Late Neogege Cuitzeo McDowell, F.W., Keizer R.P., 1977, Timing of mid-Tertiary volcanism in the Basin System (central-western Mexico, Michoacan): Paleogeography, Sierra Madre Occidental between Durango City and Mazatlán, Mexico: Paleoclimatology, Paleontology, 151, 209-227. Geological Society of America Bulletin, 88, 1479-1487. Israde-Alcántara, I., Miller, W., Garduño-Monroy, V.H., Barron, J., Rodriguez- McDowell, F.W., Clabaugh, S.E., 1979, Ignimbrites of the Sierra Madre Occidental Pascua, M., 2010, Palaeoenvironmental significance of diatom and and their relation to the tectonic history of western Mexico: Geological vertebrate fossils from Late Cenozoic tectonic basins in west-central Society of America Bulletin, Special Paper, 180, 113-124. México: A review: Quaternary International, 219, 79-94. McKenna, M.C., Bell, S.K., 1997, Classification of mammals above the species Jiménez-Hidalgo, E., Smith, K., Guerrero-Arenas, R., Alvarado-Ortega, J., 2011, level: New York, Columbia University Press, 631 pp. No evidence of caviomorph rodents in a new, Late Eocene terrestrial McLean, H., Hausback, B.P., 1984, Reconnaissance geologic map of the La vertebrate locality in northwestern Oaxaca, southern Mexico: Society of Purísima-Paso Hondo area, Baja California Sur, Mexico: U.S. Geological Vertebrate Paleontology, Program and Abstracts, 132. Survey Open File Report, 84-93. Kelly, T.S., 1994, Two Pliocene (Blancan) vertebrate faunas from Douglas McLean H., Hausback, B.P., Knapp, J.H., 1985, Reconnaissance geologic map Country, Nevada: PaleoBios, 16(1), 1-23. of part of the San Isidro quadrangle, Baja California Sur, Mexico: U.S. Kelly, T.S., 1998, New Middle Miocene equid crania from California and their Geological Survey, Miscellaneous Field Studies Map MF-1799, scale implications for the phylogeny of the Equini: Los Angeles, Natural History 1:125,000, 1 sheet. Museum of Los Angeles County, Contributions in Science, 473, 1-43. McLean H., Hausback, B.P., Knapp, J.H., 1987, The geology of west-central Keppie, J.D., Morán-Zenteno, D.J., 2005, Tectonic implications of alternative Baja California Sur, Mexico: U.S. Geological Survey Bulletin, 1579, 1-16. Cenozoic reconstructions for southern Mexico and the Chortis block: Michaud, F., Gasse, F., Bourgois, J., Quintero, O., 2000, Tectonic controls on lake International Geology Review, 47, 473-491. distribution in the Jalisco block area (western Mexico) from Pliocene to Kilmer, F.H., 1963, Cretaceous and Cenozoic stratigraphy and paleontology, present: Geological Society of America, Special Paper, 334, 99-110. El Rosario area, Baja California, México: Berkeley, U.S.A., University of Miall, A.D., 2006, The geology of fluvial deposits: Berlin, Springer-Verlag, 582 p. California, Ph.D. thesis, 126 p. Miall, A.D., 2010, The geology of stratigraphic sequences: Berlin, Springer- Kowallis, B.J., Swisher, C.C., Carranza-Castañeda, O., Miller, W.E., Tingey, Verlag, 522 pp. D.G., 1998, Preliminary radiometric dates in selected Late Tertiary Miller, E.W., Carranza-Castañeda, O., 1984, Late Cenozoic Mammal in Central vertebrate faunas from Mexico. Avances en Investigación, Paleontología Mexico. Journal of Vertebrate Paleontology, 77(2), 216-236. de Vertebrados: México, Universidad Autónoma del Estado de Hidalgo, Mixon, R.B., 1963a. Geology of the Huizachal Redbeds, Sierra Madre Oriental, Instituto de Investigación en Ciencias de la Tierra, Publicación Especial, México: Baton Rouge, U.S.A., Louisiana State University, Ph.D. thesis, 98 p. 1, Paleontología de Vertebrados, 103-108. Mixon, R.B., 1963b. Geology of the Huizachal redbeds, Ciudad Victoria, Lahiere, L., 1982, Petrology of lacustrine deposits, Juchipila Quadrangle, southwestern Tamaulipas, in Geology of Peregrina Canyon and Sierra de Zacatecas: New Orleans. Louisiana, University of New Orleans, Master’s El Abra, Mexico: Corpus Christi, Geological Society Fieldtrip Guidebook, thesis, 113 pp. 24-35. Langenheim, R.L., Frost, S.H., 1963, Upper Tertiary continental sediments at Molnar, R.E., 1974, A distinctive theropod dinosaur from the Upper Cretaceous Ixtapa, Chiapas, Mexico-preliminary notice: Geological Society of America, of Baja California, Mexico: Journal of Paleontology, 48, 1009-1017. Special Paper, 76, 209-210. Morán-Zenteno, D.J., Keppie, J.D., 2009, Synchronous 29-19 Ma arc hiatus, Lillegraven, J.A., 1972, Preliminary Report on Late Cretaceous mammals from exhumation and subduction of forearc in southwestern of Mexico: the El Gallo formation, Baja California Norte, Mexico: Los Angeles County, Geological Society Special Publications, 328, 169-179. Contributions in Science from Natural History Museum, 232, 1-11. Morán-Zenteno, D.J., Tolson, G., Martínez-Serrano, R.G., Martiny, B., Schaaf, Lillegraven, J.A., 1976, A new genus of therian mammals from the Late P., Silva-Romo, G., Macías-Romo, C., Alba-Aldave, L., Hernández-Bernal, Cretaceous, El Gallo formation Baja California, Mexico: Journal of M.S., Solís-Pichardo, G.N., 1999, Tertiary arc-magmatism of the Sierra Paleontology, 50, 437-444. Madre del Sur, Mexico, and its transition to the volcanic activity of the López, J.C., 1991, Stratigraphy and petrology of Miocene-Pliocene lacustrine Trans-Mexican Volcanic Belt: Journal of South American Earth Science, deposits, Juchipila Quadrangle, Zacatecas, México: Louisiana, U.S.A., 12, 513-535. University of New Orleans, master thesis, 95 pp. Morán-Zenteno, D.J., Martiny, B., Tolson, G., Solís-Pichardo, G., Alba-Aldave López-Ticha, D., 1985, Revisión de la estratigrafía y potencial petrolero de L., Hernández-Bernal, M.S., Macías-Romo, C., Martínez-Serrano, la Cuenca de Tlaxiaco: Asociación Mexicana de Geólogos Petroleros, R.G., Schaaf, P., Silva-Romo, G., 2000, Geocronología y características Boletín, 37(1), 49-92. geoquímicas de las rocas magmáticas terciarias de la Sierra Madre del Sur:

340 RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx Isotope geochronology and vertebrate paleontology in México

México, Boletín de la Sociedad Geológica Mexicana, LIII, 27-58. Geológicas, 25(3), 494-516. Morgan, G.S., White, R.S.Jr., 2005, Miocene and Pliocene vertebrates from Schaaf, P., Morán-Zenteno, D.J., Hernández-Bernal, M.S., Solís-Pichardo, G., Arizona: New Mexico, Museum of Natural History and Science, Bulletin, Tolson. G. Köhler, H., 1995, Paleogene continental margin truncation 29, 115-136. in southwestern Mexico; geochronological evidence: Tectonics, 14, Morris, W.J., 1972, A giant hadrosaurian dinosaur from Baja California: Journal 1339-1350. of Paleontology, 46, 777-779. Schulze, C.H., Keppie, J.D., Ortega Rivera, A., Ortega-Gutiérrez, F., Lee, J.K.W., Morris, W.J., 1973a, Mesozoic and Tertiary Vertebrates in Baja California: 2004, Mid-Tertiary cooling ages in the Precambrian Oaxacan Complex National Geographic Society Research Reports, 1973, 197-209. of southern Mexico: indication of exhumation and inland arc migration: Morris, W.J., 1973b, A review of Pacific Coast hadrosaurs: Journal of. Revista Mexicana de Ciencias Geológicas, 21(2), 203-211. Paleontology, 47, 551-561. Scott, W.B., 1937, A history of the land mammals of the Western Hemisphere: Morris, W.J., 1981, A new species of hadrosaurian dinosaur from the Upper New York, The MacMillan Company, 786 pp. Cretaceous of Baja California-? Lambeosaurus laticaudus: Journal of Segerstrom, K., 1956, Estratigrafía y Tectónica del Cenozoico entre México, Paleontology, 55, 453-462. D.F. y Zimapán, Hidalgo: México, Congreso Geológico Internacional, 20ª Nieto-Samaniego A.F., Alaniz-Alvarez, S.A., Silva-Romo, G., Eguiza-Castro, Sesión, México, Excursiones A-3 y C-1, Libro-Guía, 11-37. M.H., Mendoza-Rosales, C.C., 2006, Latest Cretaceous to Miocene Segerstrom, K., 1962, Geology of south-central Hidalgo and northeastern deformation events in the Eastern Sierra Madre del Sur, Mexico, inferred México: United States Geological Survey Bulletin, 1104-C, iii-v, 88-162. from the geometry and age of major structures: Geological Society of Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos America Bulletin, 118(1-2), 238-252. Minerales), 1991, Monografía Geológico-Minera del Estado de Zacatecas: North American Commission on Stratigraphic Nomenclature (NACSN), 1983, Pachuca, Hgo., Consejo de Recursos Minerales, 154 pp, includes a geologic North American Stratigraphic Code: American Association of Petroleum state map scale 1:500,000. Geologists Bulletin, 67, 841-875. Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos North American Commission on Stratigraphic Nomenclature (NACSN), 2005, Minerales), 1992, Monografía Geológico-Minera del Estado de Jalisco: North American Stratigraphic Code: Bulletin of the American Association Pachuca, Hgo., Consejo de Recursos Minerales, 136 pp, includes a geologic of Petroleum Geologists, 98, 1547-1591. state map scale 1:500,000. Pallares, C., Bellon, H., Benoit, M., Maury, R.C., Aguillón-Robles, A., Calmus, Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos T., Cotten, J., 2008, Temporal geochemical evolution of Neogene volcanism Minerales), 1995a. Carta Geológico-Minera Actopan F14-D71, Hidalgo, in northern Baja California (27°-30°N): Insights on the origin of post- Escala 1:50,000. Pachuca, Hgo. Servicio Geológico Mexicano-Secretaría subduction magnesian andesites: Lithos, 105, 162-180. de Economía. Pascual, R., 1972, The Cenozoic mammal fauna of South America, pp. 240-329, Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos Minerales), in Keast, A., (ed.), Evolution, mammals and southern continents: Albany, 1995b, Monografía Geológico-Minera del Estado de Michoacán: Pachuca, State University of New York, 543 pp. Hgo., Consejo de Recursos Minerales, 175 pp, includes a geologic state Patterson B., Wood, A.E., 1982, Rodents from the Deseadan Oligocene of Bolivia map scale 1:500,000. and the relationships of the Caviomorpha: Harvard University, Bulletin of Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos the Museum of Comparative Zoology, 149(7), 371-543. Minerales), 1996, Carta Geológico-Minera Dolores Hidalgo, F14-C44, Renne, P.R., Fulford, M.M., Busby-Spera, C., 1991, High Resolution 40Ar/39Ar Guanajuato, Escala 1:50,000: Pachuca, Hgo., Servicio Geológico Mexicano- Chronostratigraphy of the late Cretaceous El Gallo formation, Baja Secretaría de Economía. California del Norte, Mexico: Geophysical Research Letters, 18(3), 459-462. Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos Repenning, C.A., 1962, The giant ground squirrel Paenemarmota: Journal of Minerales), 1999a, Carta Geológico-Minera San Francisco Telixtlahuaca Paleontology, 36(3), 540-556. E14-D37, Oaxaca. Escala 1:50,000, Pachuca, Hgo. Secretaría de Economía- Repenning, C.A., Weasma, T.R., Scott, G.R., 1995, The early Pleistocene (latest Consejo de Recursos Minerales. Blancan-earliest Irvingtonian) Froman Ferry Fauna and history of the Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos Glenns Ferry Formation, southwestern Idaho: United States Geological Minerales), 1999b, Carta Geológico-Minera San Miguel de Allende Survey Bulletin, 2105, 1-86. F14-C54, Guanajuato, Escala 1:50,000: Pachuca, Hgo., Servicio Geológico Reynoso, V.H., 1996, A Middle Jurassic Sphenodon-like sphenodontian Mexicano-Secretaría de Economía. (Diapsida Lepidosauria) from Huizachal Canyon, Tamaulipas: Journal of Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos Vertebrate Paleontology, 16, 210-221. Minerales), 2000, Carta Geológico-Minera Oaxaca E14-D9, Oaxaca y Robinson, P., Gunnel, G.F., Walsh, S.L., Clyde, W.C., Storer, J.E. Stucky, Puebla. Escala 1:250,000: Pachuca, Hgo., Secretaria de Economía-Servicio R.K, Froehlich, D.J., Ferrusquía-Villafranca, I, McKenna, M.C., 2004, Geológico Mexicano. Consejo de Recursos Minerales. Wasatchian through Duchesnean Biochronology, in Woodburne, M.O., Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos (ed.), Late Cretaceous and Cenozoic Mammals of North America: New Minerales), 2006, Carta Geológico-Minera La Yesca F13-D33, Nayarit, York, Columbia University Press, 106-155. Escala 1:50,000: Pachuca, Hgo., Servicio Geológico Mexicano-Secretaría Rosas-Elguera, J., Urrutia Fucugauchi, J., 1998, Tectonic control of the de Economía. volcano-sedimentary sequence of the Chapala Graben, western Mexico: Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos International Geology Review, 40, 350-362. Minerales), 2007, Carta Geológico-Minera Oaxaca de Juárez E14-D47, Rosas-Elguera, J., Ferrari, L., Garduño-Monroy, V.H., Urruti-Fucugauchi, J., Oaxaca, Escala 1:50,000: Pachuca Hgo., Consejo de Recursos Minerales. 1996, Continental boundaries of the Jalisco Block and their influence in the Servicio Geológico Mexicano (SGM, before 2004 Consejo de Recursos Pliocene-Quaternary kinematics of western Mexico: Geology, 24, 921-924. Minerales), 2014, Carta Geológico-Minera Tecolotlán F13-D83, Escala Rubio-Cisneros, I.I., Lawton, T.F., 2011, Detrital zircon U-Pb ages of sandstones 1:50,000: Pachuca, Hgo., Servicio Geológico Mexicano-Secretaría de in continental red beds at Valle de Huizachal, Tamaulipas, NE Mexico: Economía. Record of Early-Middle Jurassic arc volcanism and transition to crustal Silva-Mora, L., 1995, Hoja Morelia 14Q-g(2), con resumen de la geología de la extension: Geosphere, 7, 159-170. Hoja Morelia, Estados de Michoacán y Guanajuato: México, Universidad Salvador, A., 1987, Triassic-Jurassic paleogeography and origin of the Gulf Nacional Autónoma de México, Instituto de Geología, Carta Geológica of Mexico Basin: Bulletin of the American Association of Petroleum de México, Serie 1:100,000. Geologists, 71, 419-457. Silva-Romo, G., Mendoza-Rosales, C., 2008, Laramide sedimentation and Sánchez-Montes de Oca, R., Bartolini, A.C., Ángeles, A.F, Espinosa E.L, Vélez, deformation along Papalutla Fault system: Geological Society of America, S.D., 1979, Geología de la Sierra de Chiapas: Boletín de la Asociación Abstracts with Programs, 40, 547. Mexicana de Geólogos Petroleros, 31(2-6), 67-96. Skinner, M.F., Skinner, S.M., Gooris, R.J., 1977, Stratigraphy and biostratigraphy Santamaría-Díaz, A., Alaniz-Alvarez, S.A., Nieto-Samaniego, A.F., 2008, of late Cenozoic deposits in central Sioux Country, western Nebraska: Deformaciones cenozoicas en la cobertura de la falla Caltepec en la región New York, American Museum of Natural History, Bulletin, 158, 263-371. de Tamazulapam, sur de México: México, Revista Mexicana de Ciencias Stehli, F., Webb, S.D., 1985, The Great American Biotic Interchange: New York,

RMCG | v. 32 | núm. 2 | www.rmcg.unam.mx 341 Ferrusquía-Villafranca and Ruiz-González

Plenum Press, 532 pp. Woodburne, M.O. (ed.), 2004, Late Cretaceous and Cenozoic mammals of North Tedford, R.H., Albright, L.B., Barnowsky, A.D., Ferrusquía- Villafranca, I., America: New York, Columbia University Press, 391 pp. Hunt, R.M. Jr., Storer, J.E., Swisher, S.C. III, Voorhies, M.R., Webb, S.D., Woodburne, M.O., Tedford, R.H., Swisher, C.C.III, 1990, Lithostratigraphy, Whistler D.P., 2004, Mammalian biochronology of the Arikareean trough biostratigraphy and geochronology of the Barstow Formation, Mohave Hemphillian interval (late Oligocene through Oligocene epochs), in Desert, southern California: Bulletin of the Geological Society of America, Woodburne, M.O., (ed.), Late Cretaceous and Cenozoic Mammals of North 102, 459-477. America: New York, Columbia University Press, 169-231. Woodburne, M.O., Cione, A.L., Tonini, E.P., 2006, American provincialism Umhoefer, P.J., Dorsey, R.J., Willsey. S., Mayer, L., Renne, P., 2001, Stratigraphy and the Great American Faunal Interchange, in Carranza-Castañeda, O., and geochronology of the Comondú Group near Loreto, Baja California Lindsay, E.H., (eds.), Advances in Late Tertiary Vertebrate Paleontology Sur, Mexico: Sedimentary Geology, 144, 25-147. in Mexico and the Great American Biotic Interchange: México, D.F., Van der Pluijm, B., Vrolijk, P., Peacor, D., Hall, C., Solum, J., 2006, Fault dating Universidad Nacional Autónoma de México, Instituto de Geología and in the Canadian Rocky Mountains: evidence for late Cretaceous and Early Centro de Geociencias, Publicación Especial, 4, 77-101. Eocene orogenic pulses: Geology, 34, 837-840. Wagner, H., 1976, A new species of Pliotaxidea (Mustelidae: Carnivora) from California: Journal of Paleontology, 50, 107-127. Wagner, G., van den Haute, P., 1992, Fission track dating: Netherlands, Kluwer Academic Publishers, 322 pp. Webber, L.K., Fernández, L.A., Simons, W.B., 1994, Geochemistry and mineralogy of the Eocene-Oligocene volcanic sequence, Sierra Madre Occidental, Juchipila, Zacatecas, Mexico: Geofísica Internacional, 33, 77-89. Whitmore, F.C., Jr., Stewart, R.H., 1965, Miocene mammals and Central American seaways: Science, 148, 180-185. Wilson, J.A., Clabaugh, S.E., 1970, A new Miocene formation and a description of volcanic rocks, Northern Valley of Oaxaca, State of Oaxaca: México, Manuscript received: October 25, 2013 Sociedad Geológica Mexicana, Libro Guía, Excursión México Oaxaca, Corrected manuscript received: February 27, 2015 120-128. Manuscript accepted: March 16, 2015

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